Pace of play
Pace of play is a concept that refers to the total time it takes to play a game of baseball, and also to the frequency of interruptions and other "dead time" during that time span.
For most of baseball history, pace of play was not a major concern, although that did not keep some people from complaining that games were too slow. Games rarely took more than two hours to complete, and while teams sometimes tried to stall intentionally in situations such as a impending rain delay or curfew, this was rare enough not to be considered a significant problem. However, the average game time has grown along a linear path since the 1910s, from 110 minutes then to 2 hours by the mid-1930s to 2 1/2 hours in the mid-1950s to three hours in 2000, and the complaints about the length of games and the plodding pace at which they are being played have grown along a similar trend. This is mainly considered an issue in Major League Baseball and not at other levels of the game such as the minor leagues, college baseball or in foreign leagues. Commissioners Bud Selig and Rob Manfred both flagged the issue as one that needed to be addressed, and began to take measures to "speed up the game".
One of the first modern observers to point towards the problem was Bill James, who was mainly concerned about the break in momentum caused by the huge increase in mid-inning pitching changes - accompanied by commercial breaks - at the tensest moments of the game. He felt this was detrimental to the game and proposed some possible solutions, but his proposals were largely ignored.
By the end of the 2000s, the issue had become impossible to avoid, and was especially salient during showcase postseason games: the combination of late starting times (for viewers on the East Coast), longer commercial breaks, and greater recourse to mid-inning pitching changes resulted in games regularly ending after midnight, and crucial innings taking an agonizingly long time to be completed. Among the measures proposed or implemented to address the issue have been: the automatic intentional walk (which hardly cuts any time, given how infrequent intentional passes have become); rules to prevent batters from stepping out of the batter's box between pitches (on the books, but largely unenforced); rules forcing pitchers to work more quickly, including the threatened introduction of a pitch clock; rules to reduce the time between innings and forcing the batter and pitcher to be ready to go immediately (again, well-meaning but ineffective in the absence of penalties for violations); a limit on mound visits (this actually had some effect without being overly disruptive); and finally a rule forcing relief pitchers to face at least three batters or finish the inning before being replaced, slated to come into force in 2020. Rules to speed up the pace of play in international play were successful when first implemented in the 2019 Pan American Games - a 20-second pitch clock, 30 seconds for a mound visit, 90 seconds for a pitching change and 90 seconds between innings. These led to an average game time around 2 and a half hours, considered a success.
Unfortunately the early results on changes at the major league level were not positive, as the games continued to get longer in the late 2010s. Most of the extra length was due, according to researcher David Smith to a change in how the game is played: with batters going deeper into the count and strikeouts significantly on the rise, the increased length in game time could be entirely attributed to more pitches being needed to complete 9 innings of play. Something that could only be changed if hitters completely changed their approach - which may eventually happen but cannot be mandated by outsiders.
- Gabe Lacques: "MLB's efforts to speed up play run into reality of modern game: 'It's not going to happen'", USA Today, September 3, 2019. 
- David W. Smith: "Why Do Games Take So Long?", Baseball Research Journal, SABR, Vol. 47, Nr. 2 (Fall 2018), pp. 64-69.
- David W. Smith: "Time Between Pitches: Cause of Long Games?", in Baseball Research Journal, SABR, Volume 48 Number 2, Fall 2019, pp. 24-28.