People have different opinions on using sports gear. IMHO I have no problem with using SOME sorts gear such as shin guards. Football padding and the like I don't think would be very acceptable. You may be able to pull off using catchers equipment, but you may have to do ALOT of mods to it. Got some pics of it?
I think someone used something like this at DragonCon last year and pulled it off rather nicely.
Since these are setmented, you think you can loose the foot guard and everything above the top of the shin? I think that would probably work ok. You can bondo the holes in the shin armor if you felt like going that far =D
The only reason I say remove the knee pieces is because if you want to have Mando style knees...then those wont work. If your not gonna do mando knees then I would suggest giving those knees a good work-up like putting spikes on them or something. You want to take away the image of *Sports equipment* and give it the Mando image.