Riggs and Murtaugh versus Lowrey and Burnett
Riggs and Murtaugh (Lethal weapon series) versus Lowrey and Burnett (Bad boys 1 and 2).
Riggs and Murtaugh (Let's go with the Lethal Weapon 3 version) are investigating a new drug trafficking ring, while Lowrey and Burnett are undercover, posing as drug dealers.
During a buy, the deal goes bad, and the bad guys flee. Riggs and Murtaugh, observing from a short distance away, rush in, sirens blaring, attempting to arrest Lowrey and Burnett. Before Lowrey and Burnett can ID themselves as Police officers, Riggs, crazy as he is, opens fire. Lowrey and Burnett dive for cover, and the battle is on.....
The combatants are armed with, let's say..... Murtaugh with a .357 wheel gun, Riggs, Lowrey and Burnett all armed with 9 mm automatics. The battle takes place in an underground parking garage filled with cars, well lit and lots of places to hide.