I think Team Player just means you can play them out of position (without changing their position) without having it affect them as much, but I'm not actually sure.
Regardless of what that trait *actually* means, I've been toying with the idea of using it as my own personal tool for which low-rated players to recruit just to change positions. Like, "this guy is willing to move to defense if it helps the team." Because it's largely a roll of the dice anyway, it doesn't seem like you can reliably scout your way into players who develop well at different positions. So if I'm going to keep doing this just for fun, I'll want something to help me decide beyond just "this guy is fast," when I have multiple options that are similarly athletic.