Here is why that the Padres trading for Mason Miller left other teams in the MLB "pissed," which includes a certain prospect.

San Diego shockingly acquired 100-mph flamethrower Mason Miller from the A’s on Thursday in a massive move ahead of the MLB trade deadline, The Post’s Jon Heyman confirmed. San Diego is also receiving former Yankee lefty JP Sears, while the A’s are receiving four players, including the No. 3 prospect in the sport in shortstop Leo De Vries.

Frost and the Athletics pulled the trigger for the Miller trade thanks to Leo De Vries' inclusion in the trade. Without him, the Athletics likely wouldn't have been interested in a Miller trade.