The Philadelphia Flyers mascot did NOT assault a 13-year-old boy ... according to Philly police, who just announced Gritty has been cleared after a weeks-long probe.
As we previously reported, a man claims his young son was punched in the back by the mascot at Wells Fargo Arena during a Nov. 19 photo shoot fan event.
Chris Greenwell -- the father of the alleged victim -- says Gritty "took a running start" and "punched my son as hard as he could" after he alleges the kid "playfully patted" the mascot on the head.