Rally Fries were started by Mariners broadcaster Mike Blowers in 2007. During a game against the Cincinnati Reds, a fan tried to catch a foul ball along the right-field line but in turn spilled his tray of french fries along the track. While chatting on the air and seeing the mishap, Blowers' partner, Dave Sims, suggested that he should send a new tray of fries to the fan. Blowers agreed, and sent his intern to deliver a plate of fries to the man.
However, on the next game, fans made signs and boards, asking Blowers for free fries as well. Coincidentally, every time the fries were delivered, the Mariners seem to score or rally from a deficit, and thus the "Rally Fries" were created.