last night l tried and some times l reached 20 miles and hour.i was running and my dad was in the car

At 20 MPH, you are running about 11 seconds per 100 meters, which is pretty fast. Of course, that is assuming the speedometer is perfectly synchronized with your running, which l doubt. Try finding a track, and timing your 100M sprint for a much more accurate reading.

true! if a ford, mine always fudged a bit 10% (makes u drive slower & think u get better gas mileage.
NOW ur answer. if u mean football, like soccer, speed is not so important. if u mean centers, quarterbacks, & wide receivers- well, do u weigh 280 pounds? nah-just kidding. l would consider muscularity (something l can not build 6'4'' 173 lbs & gave up trying.) more important than speed. u will have to carry 1/2 ton of pads & be fast, too. muscles again. ask ur coach- he may put u in as (boring) defense, but hey-you get to play. THAT IS ALL THAT COUNTS. speed may or not.
also, try 100 to 400 meter in track. best luck in sports!

best not to do both at the same time though