Finding the problem and the initial confrontation
First, let us define what being up to par means. In terms of DPS, you actually have the easiest metric out of all the other roles in determining how a player is performing: DPS meters. While there is the risk of going too far with meters and, as with anything, you need more than a single data set to go off of, using DPS meters can easily be used to track a player's performance. In this case, the comparison is not against the Top 100 or whichever other metric that whatever site uses; the comparison is exclusively against that of your own team. Nothing more, nothing less.
Always make comparisons within house; never even bother with what you see other players performing at. You don't know what strategy those players are using, you don't know their gear setup, and you don't know what weird or strange mechanics may be involved with their parses. There are simply too many unknown factors involved. Within any raid team, everyone's DPS should create a neat average, and every player should be within an acceptable range of that margin.
When faced with a lack of progression to the point that you evaluate keeping a player a part of the team or not, always be direct with the player. Pull him aside before or after a raid -- preferably the latter -- and express your concerns. Be nonconfrontational and allow him to defend himself, but by the same token be firm. Don't tell him that he sucks or that he's bad; just say that his DPS isn't up to the average of the rest of the raid and that he has a time frame of X to correct it or his spot is going to be taken by another player.
Set realistic goals -- I would give a player two weeks -- and for the love of Elune, stick to them. If you tell a player that he has two weeks to shape up, then he has two weeks to shape up -- not three, not four. Two.
Dealing with excuses
Now, when going into this conversation, there are a few things that you need to be ready for. First is that he will certainly defend himself. Some people are more passive, but I have yet to see a single player who just says, "Yes, my DPS is unacceptable; I'll fix it." Players are going to defend themselves, but you cannot allow yourself to buy into these arguments. Unacceptable DPS is purely that -- unacceptable. There are no excuses for it. Here are the more common lines you'll hear.
It isn't me -- it's my spec! More commonly, this comes from hybrid classes, but pures use it just as much these days. In every single example, it is nothing short of bollocks. In this day and age of WoW, there is not a single spec that I have seen whose simulated DPS is so poor that a player using it is going to parse so far below the normal average of a raid. As an example, the current destruction warlock spec simulates as being around 3,000 DPS less than affliction. This is in perfect conditions with people performing perfectly. This is not going to happen within your raid. The average and even the good player is not going to change his spec from destruction to affliction and suddenly see a 3,000 jump in DPS. It doesn't work that way.
For starters, no player performs to the absolute best of his spec's ability. None. You can simulate until the sun burns out; it just doesn't matter. Encounter mechanics alone will prevent a player from performing at the most optimal level, and from there it only goes downhill as he starts to make minor mistakes. Each mistake in a rotation leads to far more DPS loss than anything else. The little, inconsequential mistakes that most players make in their rotation during an encounter account for all of the damage that their talents give them combined. A perfect player could have spent no talent points and perform better than a fully specced player who only makes a few mistakes.
Spec never has been and never will be an acceptable excuse for poor DPS performance. Players of all types have been proving that since vanilla. A fantastic player can take any spec and beat the pants off of an average player, no matter what spec that he plays.
Further, in many cases, DPS is all about skill cap. Skill caps used to be the big buzzword back during a portion of Wrath, but it is a concept that has rather died off since then. Essentially, not all specs are created equal. While there may be a 3,000 DPS difference between a perfectly played affliction and destruction warlock, due to skill cap differences, there would probably only be a 1,000 or less DPS difference between average players of the same time. Skill influences each spec differently, and it's a huge scaling factor that many simulators just don't take into account. Precise timing accounts for more DPS for one spec than it does for others.
Lastly, if you know that you spec is holding you back so much to as risk your position within a raid, why play it? I fully understand that players want to play the spec that's the most fun to them -- hell, I'm a vanilla balance druid, and those didn't even exist back then -- yet there just has to be somewhere that you draw the line. At some point, a player has to say to himself, "I love this spec, but it just isn't viable at this point in the game." It sucks, and we all hate it, but there are just times where you have to deal with.
These bosses just don't support my spec.
Encounter design plays a huge factor in which specs succeed or fail, this is true. Certain specs just have that one ability or talent that's spectacular for a boss fight and causes it to pull miles ahead of others. This happens all the time; it has been happening since the very first raid, and it will keep on happening. Good raiders and good players have to learn to be adaptive. Maybe you hate playing survival, but if survival hunters can make use of unique encounter mechanic to push an additional 5,000 DPS, then frankly we've reached a point where it doesn't matter what you want anymore.
It may seem crass and rude, but raid leaders have to understand that they can't always worry about the feelings of a single player; they have an entire raid of players, plus people on standby, that they have to think of too. If you have reached a point where you just can't down a boss because your DPS isn't there and you have a raider who is refusing something so basic as to switch specs for a single fight where that spec offers such a huge benefit, then it is time for that player to go.
Frankly, I do not even see how someone can justify using this excuse. This might be horrible of me, but it is true. In the day where two dailies can pay for a respec, when there are dual specs, how can any raider sit back and be content with themselves to say, "I know that going spec X for this one
encounter would be a massive help to my raid, but I only play as spec Y, and I'm not changing specs." Make no mistake, that is exactly what these people are saying. Sure, I'm certain they word it a more flattering light, but that's the general meaning.
I'd be fine if only I had Item X.
During my time as a raid leader, I got this retort quite often, and it is the only one that has ever given my any pause. Itemization is something of a double-edged sword in many cases. At the surface, this excuse has no foundation, but there are rare exceptions.
First and foremost, itemization almost never makes or breaks a spec -- it always comes down to the player -- yet there are times that certain items can have a huge impact on a player's performance. As an example, the current elemental shaman raiding tier offers a huge damage bonus. The old balance druid tier was similar, with the four-piece being worth thousands of DPS.
Any time that I hear this used, my first counter-question is to ask why they don't yet have the item. Drops can be hell, I will not deny that at all, yet by the same token, it should be equally bad to everyone involved. You shouldn't even be in a position where a single mage or a single warlock is far behind the pack because of a single item drop. Gearing simply isn't that important. No matter how much DPS an item is worth to a player, it just isn't going to account for their performing well below average. If anything, you're now in a situation where a player is underperforming and they want to use an item to mask that.
What happens when you reach the next raiding tier and that item isn't as overpowered as it once was? As they slide back down to the point that they're no longer holding their own, what do you do? Certain items can hold a vast impact on damage in very specific situations, but it will never do more than mask the failings of a player who isn't performing at the same level as the rest of the raid. In these situations, the player should likely be average without and pushing the top of the pack with it.
You can't be everyone's friend
I know that most of this can seem very harsh, but you have to understand the position that raid leaders are put in when raids stop making progression. All of this content is designed so that it can be done; when you can't do it, you really have to look at why. Most every encounter created relies upon the DPS far more than any other role. Low DPS can cause trickling issues in the raid that can make it appear as though you have a different issue, but the truth is plain.
As a raid leader, you can't always be everyone's friend; there are going to be times when you have to be the bad guy. Having a DPSer who is lagging behind the rest of the pack is an issue that effects the raid as a whole, and it's your job to make sure that it is corrected. These players have to be confronted, and while the thought may seem unappetizing, it's a part of the job that you must face.
Be direct; be firm. Tell the player in question the issue, offer to work with him, give him a chance to improve his performance, but don't buy into what he's selling. Players hate being called out, as it were (and who wouldn't?), yet it must be done. Do it, and be prepared for their fast talk to get out. Harsh as it seems, they are but one player; you've got nine or 24 others to look out for as well.
Ready Check shares all the strategies and inside information you need to take your raiding to the next level. Be sure to look up our strategy guides to Cataclysm's 5-man instances, and for more healer-centric advice, visit Raid Rx.