Major League Baseball issued a memo on Wednesday to clarify rule changes that have shaved the average time of pre-season games by 25 minutes ahead of next week's 2023 season openers.

The details were mainly about the new pitch timer and about defensive infield shift restrictions, which, along with slightly enlarged bases, have been approved for the upcoming campaign that begins March 30.

Basic changes remain the same with 30-second pitch clocks – pitchers have 15 seconds on the mound to throw with no base runners, 20 seconds with runners on base and batters must be "alert" in the batter's box with eight seconds remaining on the clock.

Average spring training games have taken two hours and 36 minutes – down 25 minutes from last year's pre-season games. Clock violations have fallen to 1.03 on average per game from 2.03 when tuneup contests began.

The guidance came after input from the MLB Players' Association as well as questions from umpires and teams during the month of pre-season contests.

A batting team will now be allowed to make a replay review challenge using the defensive positioning rule only against the first infielder to touch the ball on a play.

Before, batting teams could try and catch any fielder with his feet on the outfield grass to negate an out.

Batters who are knocked down or brushed back by a pitch will be allowed to gather themselves and readjust equipment before the clock starts.

Pitchers forced to field other positions during a play, such as backing up fielders at third base or home plate, will be granted a delay before the start of the 30-second clock between pitches.

Catchers who have made a "reasonable effort" to comply with inning break rules after being left on base or at bat will be given additional time to reach their fielding position at an umpire's discretion.

Batters will be allowed one timeout for each plate appearance and will be allowed to indicate to umpire's they are ready for the timer to be reset, so they are not required to be in the batter's box for 20 seconds or more.

Should the clock malfunction, pitchers or catchers should ask for a timeout and notify umpires. (AFP)