Keenan Allen's got a little bit of Marshawn Lynch in him -- 'cause after the Chargers WR lit up the Seahawks on Sunday, he busted a crotch grab aimed right at some Seattle fans!
TMZ Sports has the footage showing Allen walking toward the tunnel after L.A.'s 25-17 victory over Seattle ... and grabbing his junk while staring at some loud Hawks fans at CenturyLink Field in Seattle.
After two solid pumps -- Allen playfully stuck out his tongue at the fans and continued into the locker room.
Allen had a helluva game -- hauling in 6 catches for 124 yards and 2 rushes for 28 yards.