UTIL PlayerByIndex

CBasePlayer *UTIL_PlayerByIndex( int entindex ) { return ToBasePlayer( ClientEntityList().GetEnt( entindex ) );

Players entities range from 1 - MAXPLAYERS, and non-players entities start at MAXPLAYERS + 1. I.E if A joins (1), then B joins (2) then A leaves 1 will free up, Player C joins (1)

(much thanks to DaFox for providing this information).