The record for the most number of pitches in one at bat is 20. The feat took place on June 26, 1998, with Bartolo Colon of the Cleveland Indians facing Ricky Gutierrez of the Houston Astros.
When Gutierrez stepped up to the plate against Colon, the Indians were beating the Astros four to two in the eighth inning with none out. Colon quickly fell behind in the count with no balls and two strikes, but it would take a staggering 18 more pitches for Colon to strike Gutierrez out. It took 13 pitches just to make it to a full count. This single-plate appearance represents 18 percent of all the pitches Colon threw that day.