This Sunday Dan Cosgrove needs to run a roughly 7-minute mile for 26 straight miles, or else he’s going to give away a bunch of Hawaiian shirts.

Cosgrove is the co-founder of Boston-based Fielder’s Derby, a lifestyle apparel brand that makes fun and comfortable Hawaiian shirts. Cosgrove is running the Chicago Marathon this week and plans to give away a free shirt to anyone who buys one from now until race day if he fails to run the marathon in under three hours and five minutes. (This is his third marathon, and he’s never made it under 3:05, so he admits there’s a decent chance customers will cash in on the 2-for-1.)

“I need to really make sure I dont hit the damn runners wall,” he told me over email.

But more than a fun promotion, Fielder’s Derby sees the Chicago Marathon as a chance to give back. 10% of the company’s sales from now through the end of October will go directly to breast cancer research. It’s a cause that hits home for Cosgrove, whose mother is a breast cancer survivor.

via Fielder’s Derby

“(My mom) deserves all the credit in keeping me alive and giving me all the opportunities in the world to be successful in my life,” he said. “I am grateful everyday that she won her fight with cancer and so for me to be able to raise more money and donate more to #kickcancersass is an honor.”

“We want to play a positive role in helping find a cure for cancer,” he added.

Fielder’s Derby launched in August of last year and is named after the infield at the Kentucky Derby, which is known as the vantage point for a slightly more casual race-day viewer than the stuffier seats on the outside of the track. The company’s shirts feature some combinations you don’t normally see on Hawaiian shirts, like sharks and skis and elephants and surf boards.

“Fielder’s Derby is an infielder’s perspective of the race,” Cosgrove said. “Through our designs we hope to convey this mentality; one of having a good time while not taking ourselves too seriously.”

As for the marathon, Cosgrove said he’s trying to qualify for the Boston Marathon so he’s working hard to finish under 3:05, but notes that it’s basically a coin toss on if he’ll actually succeed.

“Getting under 3:05 will be a challenge,” he said. “I put my odds at 50/50 and will depend greatly on the weather conditions and just how I am feeling on race day.”

Images via Fielder’s Derby