The bloody footprints seen on the canvas at the end was from the Property Assistant/Intern Mark Kern, whose large feet (size 14) were painted with fake blood repeatedly so he could stomp around leaving the marks.
Neither Sasha Mitchell nor Michel Qissi ever touched real broken glass during the final fight scene: the "glass" worn on their fists is actually silicone ice, and a fake human arm (cast from the fist of props coordinator Tighe Barry)was used in the shot wherein David Sloan rubs his fist into the container of glass shards.
During the Brian Vs. Tong-Po fight, Tong-Po lifts the referee onto his shoulders while wearing a pair of boxing gloves. Yet when you see the referee being thrown over the top rope and out of the ring, you see him being thrown by a bare pair of hands.
When Jack quickly disarms Sanga's bodyguard near the end of the movie, the bodyguard doesn't flinch or even makes eye contact with Jack. He stands perfectly still while staring into the distance until he is punched and knocked down.