Because they score more points than the other team.
they need 2 safeties
2 Points. A winning team could triumph by scoring a safety and no other points.
Yes, many. Every time you hear a final score like '7 to nothing' it means one of the teams scored zero points.
Safety and a 2-point conversion
Chelsea, in the 2005/6 season, finishing with 105 points
To score more points (Goal) than the opposing team by the end of the alloted time.
A safety or by tackling the opposing team in your end-zone while they have the ball.