Conversation so far:
How was Bill Russell as a competitor?
Russell was driven by a neurotic need to win, as his Celtic teammate Heinsohn observed. He was so tense before every game that he regularly vomited in the locker room.
How did other athletes like Bill Russell?
Opponent Wilt Chamberlain said Russell's timing as a shot-blocker was unparalleled. Bill Bradley—Russell's Knicks opponent—wrote in 2009 that Russell was the smartest player ever to play the game [of basketball].

Question: What aspect of the game was he the best at?
Self-contained rewrite: What aspect of the game was Bill Russell the best at?