I was introduced to the term bullpenning by former Kane County Cougars announcer Wayne Randazzo. Now with the New York Mets broadcast team, Randazzo noted that when MLB pitchers were on Midwest League rehab stints, the presumed starter, who lost the first inning or two to the MLB arm, often performed better than expected in his new environs. Even I disagreed with the idea at first, but it now has legs into the World Series. It’s here to stay. It appears even major college programs have taken to bullpenning.
Midweek games, or non-conference games smooshed between three or four game weekend get-togethers, have long been havens of bullpenning.