Ten yards.
10 yards
10 Yards is the First Down.
10
Seriously...? Its 10
10
You need to count and make sure there aren't to many players on the field. Also, you have to go 10 yards to get a first down; So if you are on a third down and 5 yards to go for a first down you would know you have 2 more chances to go 5 more yards.
15 yards and an automatic first down.
In a normal set of downs, the ball must be advanced (by play or penalty) 10 or more yards to get a first down.
In football, you have 4 down or attemps to get so many yards, a third down conversion is where you failed to get the amount of yards on first down and second down then reach it on the third, making it first down again
11 yards to Wes Welker
10 yards for offensive holding, 5 yards and an automatic first down for defensive holding.
10 yards