Never seen anything like that so I doubt fighting but anythings possible.
I agree, if it were from fighting, I would think such injuries would be more common... And I cannot picture a scenario in a turkey fight that would cause such extensive damage to the back of the legs?
I agree with Dublelung in that it looks like he could have gotten tangled in a fence... A few years back, I bumped some birds, and one ran through some downed (coiled) barbed wire... She got caught up pretty good, and was trying to run and fly out in a panic... I did not approach in fear of making the situation worse, and she was able to free herself....
I would think predator next... Maybe a bobcat getting a hold of a flushing bird that escaped?