To be considered a blocked kick. Or has the definition of "blocked kick" when it's an open field kick changed? AFAICT it made a difference only in that the touching didn't put players of the kicking team onside. (That's long been a difference between Canadian football & rugby. In rugby you can really be strigged if you just deflect an opponent's kick slightly -- puts them all onside!)

When Fed had return kicks (i.e. kicks following CoP during a down), the spot of the kick was used like the neutral zone in determining the rights of the teams to the ball and fair catch.