I like to imagine what kind of operation they're trying to bust while going 'undercover' dressed like a Spanish Taekwondo instructor and a Crusades-era Gridiron player.
Undercover Cops was originally released in arcades in March 1992 in North America, and in Japan in July 1992. It is Irem's first attempt in the modern beat 'em up genre that was founded by Data East’s Kung-Fu Master. Players control "city sweepers", a police agent-like group who fight crime by taking down thugs in New York City in the year 2043. An American localization for the Super NES was planned, but canceled. The unreleased American version was reviewed in Vol. 58 of Nintendo Power.
Missions & Bosses: 0:20 Mission 1: Beach and Harbor 3:07 Boss 1: Parcs the Cyborg 4:10 Mission 2: Subway Platform, Elevator, and Construction Site 10:06 Boss 2: Fransowors the Biker Queen 11:55 Mission 3: Sewers 15:27 Boss 3: Moguralian (β) 17:10 Mission 4: City Streets, Alley 23:07 Boss 4: Balbarotch the Indian Mystic 24:35 Mission 5 (Final Mission): Devastated City, Crater Tunnel, Helicopter 37:01 Fight Black Clones of Players 38:21 Final Boss: The Mad Scientist, Dr. Crayborn 39:22 Good Ending & Credits (Crayborn must drop the bomb to trigger the bad ending.)
"Boss, against all expectations, the women who bounce around on one leg and attack by hurling one foot over the back of their head like a contortionist were strangely ineffective against the police officers trained in martial arts."
I just tested this, and all I did to get second player in the game was press the start button for player 2 and 1. By default, these are the "1" and "2" keys. It looks like the dipswitch is set to 2 players by default, so you would need to change that if you wanted 3 players.