I'm doing a little bit of research for a project.
Basically, for a fighting style that consists mostly of punches, what are the pros and cons of body-fitting pants (trousers, not overly tight skinny jeans etc), and those that are more on the baggy side (cargo pants, loose jeans and such)? Does this answer change if we introduce kicks and grabs?
As far as I know, footing is really important even in boxing, hence, this question.
Neither, you should be looking for something that does not restrict your move set.
If your main protagonist is wearing a tight t-shirt, then as soon as he throw a big punch, there's gonna be a ripping sound as the t-shirt shears a la Hulk. If they are wearing a tight fitting pencil skirt, any kicks is going to be impeded, the skirt will tear, and their underwear will show.
Other things to consider are things like keys in pockets as falling on them might cause injuries. Doing break falls with those in your trouser pockets is inadvisable unless the situation really demands it. Ditto with phones, chain-wallets, and other things attached to one's trousers.
You might want to browse no nonsense self defense as it is good source material.
Body-fitting: The only possible pro I can see is jock support. But this is achieved in a number of ways with loose shorts as well, so it may not be very valid. The other reason for wearing body-fitting clothes is aerodynamic advantage (think swimming, cycling)- not much of a concern in martial arts.
Loose: The biggest pro is ventilation, which keeps body temperature in check and allows you to fight longer. Besides, it allows rapid stance changes much more than tight trousers would.
I don't foresee a change in case of kicks/grabs. Maybe in a street fight situation (not controlled sport), something baggy could get caught on nearby objects.
