Pace of Play
A number of changes have been implemented to improve the pace of play since the 2014 season.
The batter's box rule -- which requires hitters to keep one foot in the box during their time at bat unless one of a group of exceptions occurs -- has been more strictly enforced since the 2015 season.
Also in 2015, timers were installed in Major League stadiums to measure the break time between innings and pitching changes. MLB lowered the time between innings to 2 minutes for local broadcasts and nationally televised games in 2019. MLB had instituted times of 2 minutes, 5 seconds for local broadcasts and 2 minutes, 25 seconds for nationally televised games in 2016, decreasing these times by 20 seconds from where they were previously. Prior to the 2018 season, MLB established a separate time of 2 minutes, 55 seconds for tiebreaker and postseason games.
As of 2018, the umpire's signal for the final warmup pitch comes at the 25-second mark and the pitcher must throw it before the clock hits 20. The batter will be announced at the 20-second mark and the pitcher must begin his windup to throw the first pitch of the inning within the five seconds before the clock hits zero. The pitcher can take as many warmup pitches as he wants within these countdown parameters.
For between-innings breaks, the timer begins when the final out of the inning is recorded, with several exceptions. If the pitcher is on base, on deck or at bat when the inning ends, the timer begins when the pitcher leaves the dugout for the mound. If the catcher is on base, on deck or at bat when the inning ends, the timer begins when the catcher enters the dugout (another catcher can begin warming up the pitcher). If the final out of the inning is subject to replay, the timer begins when the umpire signals the out. And for any extended between-innings event previously approved by the Office of the Commissioner (such as the playing of "God Bless America"), the timer begins at the conclusion of the event.
The timing clock also applies to pitching changes and begins as soon as the relief pitcher crosses the warning track (or the foul line for on-field bullpens). Players can be excused from these time limits if a delay in normal warmup activities occurs due to no fault of the players, or the umpire believes a player would be at legitimate risk of injury without receiving additional time.
In 2016, MLB began limiting mound visits -- which previously had no limit -- to 30 seconds starting when the manager or coach has exited the dugout and been granted time by the umpire. As of 2019, clubs are limited to five mound visits per team per nine innings, with teams receiving an additional visit for every extra inning played. Any manager, coach or player visit to the mound counts as a mound visit, though visits to the mound to clean cleats in rainy weather, to check on a potential injury or after the announcement of an offensive substitution are excepted. Normal communication between a player and pitcher that doesn't require either to vacate his position on the field doesn't count as a visit. If a team is out of visits, the umpire will have discretion to grant a brief visit at the catcher's request if a cross-up has occurred between the pitcher and catcher. A rule limiting the number of mound visits to six per nine innings was first established in 2018 before being lowered to five in 2019.