This is very interesting, and sounds much more likely. It then has the opposite meaning from the one I proposed. I hope that we can have more context from the original poster to confirm this answer (which I believe is correct),In my chess playing we say what I would spell "sac" but pronounce as "sack," as a shorthand for "sacrifice".
"He sacked his bishop and rook to force mate."
My bet is that the citation is a report from an interview, an oral statement, that the recorder wrote as "sack."
This must have been said in jest, as Bobby was not a wild, sacrificial player. What's intended is that to win you must play aggressively, maintaining the pressure on your opponent at all times. "Sack" often "sac" is short for sacrifice. Bobby, however, did not sacrifice pieces in the way that Russian former World Champion Tal did.According to chess GM Bobby Fisher, you have to "sack, sack and sack". Please, what did he mean?