What was found
NOSE GEAR WOULD NOT RETRACT REPORTED BY FLIGHT CREW , AIR RETURN. UPON PARKING AT GATE 17 IN EWR DISCOVERED N/L/G PIN INSTALLED. FLAG WAS FULL OF GREASE. REMOVED N/L/G PIN, CLEANED FLAG, STOWED PIN AND ENSURED ALL GEAR PINS WERE REMOVED AND STOWED IN FLIGHT DECK POUCH.