Small and with a fishtail and fins, he is a goalkeeping genius defying physical laws.
1840, from fish (n.) + tail (n.). As a verb, 1927, originally of aircraft, later automobiles. Related: Fishtailed; fishtailing.
To swing a car, motorcycle, etc, from side to side at the rear: causing his rear wheels to spin or the rear end to fishtail, that is swing back and forth (1927+)