Major League Baseball has implemented significant pace-of-play rule changes for the 2015 season in an effort to speed up the game, it was announced Friday.

The rules include mandating that managers stay in the dugout during replay challenges, that hitters keep at least one foot in the batter's box during at-bats, a prompt return to play after TV commercial breaks and timed pitching changes.

"These changes represent a step forward in our efforts to streamline the pace of play," MLB commissioner Rob Manfred said in a statement. "The most fundamental starting point for improving the pace of the average game involves getting into and out of breaks seamlessly. In addition, the batter's box rule will help speed up a basic action of the game."

The league, which announced the changes with the MLB Players Association,  established a pace-of-game committee in September aimed at making recommendations to speed up games, which grew to a record average of 3 hours, 2 minutes in 2014, up from 2:33 in 1981.

Players who violate the rules will receive a warning, with "flagrant violators" subject to a series of fines up to $500, sources familiar with the changes told ESPN.com's Jayson Stark. The intention is not to impose penalties but rather to help change the habits of current players in an effort to speed up the game, sources told Stark.