The big circle is called a Scrummage.
It is when both sets of forwards attempt to drive the other off the ball so their team may gain possession. When the ball is in the scrum the players may only use their feet to touch it, and kick it back to their side.
The team who puts the ball into the scrum is the one moving forward, or the one that has the advantage when the game was stopped, either in a stalemate in the game or minor infringement by the other side.
Name: Steve
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Comments: I've played both rugby and American football. Both are tough sports. Football is more collision intensive, though, as the game is played in 10-yard (first down) increments, which requires heavy momentum-stopping collisions on a regular basis. Rugby has more flow and ball control. American football played full-speed without pads would be deadly. Take the time to read about why US colleges quit football and went back to rugby in early 1900's due to too may fatalities in football games without pads and helmets.