"Team player" is a label used to verbally pat someone on the back—or more often to verbally denigrate someone; "You're not a team player."
The problem is that nobody really knows exactly what a team player is. For example, if a person isn't willing to put up with silliness such as the currently popular so called personality or coworker compatibility tests and other useless managerial "team building" nonsense they're automatically not a team player. This is viewed as a Bad Thing® that makes him a substandard employee even if he gets more work done than the rest of the "team" combined.
It is an unfortunate reality that frequently the most productive people become the "bad guy" at least in some people's minds, simply because they know how to be productive, which certainly includes "not suffering fools" or putting up with time wasting nonsense.
In fact, all too often being significantly more productive than your so-called teammates gives them cause to resent you and want to get you to purposefully lower your productivity to match theirs so they don't look bad. If you refuse to give in to that pressure it's not a great leap for them to try to make life difficult for you and even get you fired. A significant first step toward that goal would be to get you labeled as not being a team player.
All this and more makes the catchphrase useless, or worse than useless depending on the circumstances.