Generally speaking, at most ranges where F-class matches are shot, you will drive your car down to the pits when it's your turn to pull targets. There are some exceptions at very large matches like the national matches at Camp Perry and Midwest Palma at Lodi, WI where there would be too many cars to fit into the liter parking. At those matches, a trolley, bus, etc is always provided. There may be a match somewhere where walking is mandatory, but I'd have to think that any match director worth their salt will be able to accommodate someone with a legitimate physical issue. Don't let the leg keep you from trying a match, you most likely enjoy it very much.
Good luck,
Erik