Conversation so far:
What is the pine tar incident?
Yankees manager Billy Martin cited to the umpires a rule that stated that any foreign substance on a bat could extend no further than 18 inches from the knob.
What happened after that?
The umpires measured the amount of pine tar, a legal substance used by hitters to improve their grip, on Brett's bat; the pine tar extended about 24 inches.

Question: What did he do?
Self-contained rewrite: What did George Brett do in reaction to the measurement pine tar on Brett's bat?