On July 24, 1983, the Royals played the Yankees at Yankee Stadium. In the top of the ninth inning with two out, Brett hit a go-ahead two-run homer off of Goose Gossage to put the Royals up 5-4. Upon Brett crossing the plate, 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. 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. The home plate umpire, Tim McClelland, signaled Brett out, ending the game as a Yankees win. In a now famous image, an enraged Brett charged out of the dugout sprinting directly toward McClelland and had to be physically restrained by two umpires and a Royals coach.  The Royals protested the game, and American League president Lee MacPhail upheld the protest, reasoning that the bat should have been excluded from future use but the home run should not have been nullified. Amid much controversy, the game was resumed on August 18 from the point of Brett's home run and ended with a Royals win.  In 1985, Brett had another brilliant season in which he helped propel the Royals to their second American League Championship. He batted .335 with 30 home runs and 112 RBI, finishing in the top 10 of the league in 10 different offensive categories. Defensively, he won his only Gold Glove, which broke Buddy Bell's six-year run of the award. In the final week of the regular season, he went 9-for-20 at the plate with 7 runs, 5 homers, and 9 RBI in six crucial games, five of them victories, as the Royals closed the gap and won the division title at the end. He was MVP of the 1985 playoffs against the Toronto Blue Jays, with an incredible Game 3. With KC down in the series two games to none, Brett went 4-for-4, homering in his first two at bats against Doyle Alexander, and doubled to the same spot in right field in his third at bat, leading the Royals' comeback. Brett then batted .370 in the World Series against the St. Louis Cardinals including a four-hit performance in Game 7. The Royals again rallied from a 3-1 deficit to become World Series Champions for the first time in Royals history.

Answer this question "What is the pine tar incident?" by extracting the answer from the text above.
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.