Other mistake: When Bobby recovers the onside kick, he recovered it on the 43-yard line, which is where the ball is spotted (the scoreboard even shows this). However, there was an unsportsmanlike conduct penalty with the late tackle (and a flag was thrown so we know the ref didn't miss the penalty) so the ball should have been spotted on the 28-yard line. (And there's no question there were no off-setting penalties).
Other mistake: At the beginning of the movie when Bobby starts being waterboy for Coach Klein, the players are on the field giving him a hard time. Bobby is on the sideline and the quarterback is making fun of him, which winds Bobby up and he runs onto the field tackling the quarterback. Even though Bobby hits him from the front, knocking him onto his back, a clump of grass somehow appears in the quaterback's facemask.
Answer: Didn't see the movie, but I looked up the specifications for the John Deere model 200 on TractorData. It was the first of the series and manufactured from 1975-1976. It had a Kohler one-cylinder 305cc 8 HP 4-cycle engine that runs on regular gas and a surprising maximum speed in 4th gear of 7 miles per hour! No one seems to rate lawn tractor MPGs, but similar-sized engines running generators at full load might use about 3/4 to 1 gallon per hour. So, he should be able to go at least 3 and 1/2 hours on a tank, or about 25 miles. He could fill up at a gas station without having to add oil to the gas.