Wow, I am going to take a stab at what this is as I have never seen this instrument myself
It would appear that the apparatus the one man is holding is "shooting" out something very cold, such as liquid nitrogen in a can. This is a sports scene and the area the other man is "spraying" on the apparent injured man, is the lower back. It would appear to me that the injured man was suffering from a common, well known, very painful, sciatica attack.
If you have never had one before and all of a sudden you do, your body does not recognize "the instant pain" or the pain threshold at first. Its only when you experience your first one and heal from it does your brain than recognize the onset to prevent another. Basically a sciatica attack are muscle spasms caused by, usually, a slipped vertebra disk somewhere in the mid to lower spine. The sciatic nerve runs thru the spinal column and splits in the lower back, over the butt, into each leg and downward. Lower back massage and ice, help "unstick" the muscle that is going into spasm. Once you have your first, your back has now been "injured" for life
When I had my first one back in 2000, I dropped to the floor, literally stuck in position, I didn't know what the fuck was going on, the most pain I have ever felt in my entire life. I suppose whatever the man is spraying, instant cold therapy to help alleviate the lower back muscle spasm, while on the field. The injured man is on his knees which is indicative of a first sciatic attack. Its not funny at all, once you have suffered your first, the other are more preventable. I went through muscle relaxers, physical therapy and eventually as a preventative exercise, picked up yoga
Every time "I feel the on coming sensation", I usually hit the floor and do plank pose to cobra pose to prevent on set of spasm