The Philadelphia Flyers say they found NO evidence to prove team mascot Gritty assaulted a 13-year-old boy in Nov. ... but now cops are investigating.
The Philadelphia Police Dept. has confirmed they're looking into a claim that the person inside the official Gritty costume punched a kid in the back at Wells Fargo Arena (where the Flyers play) during a Nov. 19, 2019 photo shoot fan event.
Chris Greenwell -- the father of the alleged victim -- told the Philadelphia Inquirer his son had "playfully patted" Gritty on the head after taking a picture ... but Gritty responded with real violence.
Greenwell claims Gritty "took a running start" and “punched my son as hard as he could" ... injuring the child.
The boy went to a chiropractor for treatment where he was diagnosed with a back bruise, according to Greenwell.
Greenwell says he attempted to remedy the situation through communication with officials from Flyers ownership ... but after talks soured between the two sides, he went to cops.
A Flyers spokesperson has issued a statement saying, "We took Mr. Greenwell’s allegations seriously and conducted a thorough investigation that found nothing to support this claim."
When reached by TMZ Sports on Wednesday ... Greenwell told us he's NOT considering a lawsuit against Gritty, adding, "I'm letting the police handle it."
As for the identity of the person inside the Gritty costume -- we asked cops for his name so we could reach out to him or her directly ... but so far, we haven't gotten an answer.