In rap jargon, one who hates (i.e. causes duress or abuses) a player. Especially used to refer to those who engage in cockblocking.
For a rebuttal of this term, see the lyrics of the Black Star song, Hater Players. A quote from Talib Kweli on the origins of the term:
"I first heard the term 'player hater' in Cincinnati, Ohio, many years ago. I always thought it was a curious expression. We started to see cats shouting 'player hater' to anyone who had nerve to critique they whack shit. A lot of rich players are making whack-ass music, that's the bottom line! I remember when the worst thing you could be was a sell-out. Then the sell-outs started running things."