Most of the Slow Drags I participated in were at the annual Jerome Jamboree, a VW bus ralley. The "track" was about 100 yards long, and there were 2 lanes. The rules were once you let the clutch out at the start, you couldn't touch it again, or you were disqualified. Referees would walk along each car to make sure you didn't use the clutch. If you stalled, you were disqualified. Guys would pull one plug wire, turn down the idle to where the motor would barely run, etc, to gain any advantage. A buddy once fitted some wheelbarrow tires on the back, to lower his gearing. Worked great, except the turn-around lane that year was on a hillside littered with jagged rocks, and the rocks ripped out the sidewall of the wimpy tires!
The one motorcycle slow drag I was in was probably 100 feet long, in a dirt parking lot, 3 bikes wide. You could slip the clutch, but if you put a foot down, you were disqualified. I lost the first round when a gal on a Sportster next to me swerved into my lane, causing me to put a foot down after taking evasive action. It really is great fun!!!