Knowing how to survive. What i mean by this is a player that knows what to do if anything goes wrong, always thinking ahead, a plan b, whatever you want to call it, a player that knows when to revive someone or when not to( ex: 3 ppl are down, you have good perks and a good wep maybe, you try and go to revive him and maybe going down while reviving him(you knew you probabbly were going down) now, the person you just revived has: no perks, maybe is not a skilfull player and will just try to revive you again and that leads to an inevitable lose. A player that assumes the "leader" roll of the game and always trying to give advice to the team and telling them what to do(not in a bad way).
That is to me, a pro player