My confusion comes about because I don't know what football means here. If it is American style football, in a recreational setting, then they could be playing flag football and the phrase is referring to pulling the flag off of the opponent.

2.5 FLAGS
Each player on the field will wear 2 flags at the waist, one on each side. Flags must be attached to a belt and the belt will be worn snug around the waist to eliminate being turned partially around the waist during an attempted deflagging.
http://www.texasflagfootball.com/pdf/rulebook2000.pdf

THE FLAG BELT: All shirts must be tucked in, and are not permitted to hang over the flag belt. Should a player loose their flag belt legally or illegally during a down and should that player gain possession of a live ball, that player will be considered down when a legal tag (one hand touched by the defense between the shoulders and knees, including the hand and arm) is made. When a player scores they must immediately raise their hands and allow an official to remove their flag belt. This is done to insure that the flag belt has not been illegally secured. If the belt has been illegally secured the score is disallowed, the player ejected and a 10 yard Unsportsmanlike Conduct penalty will be administered from the previous spot. Players must have possession of the ball before they can legally be deflagged. It is illegal for a defensive player **to intentionally pull a flag from an offensive player** who is not in possession of the ball. In cases where a flag belt is removed illegally, play should continue with the option of the penalty of the play (Penalty: Personal foul, 10 yards).
http://www.ruf.rice.edu/~ims/rules/flag.html

Defenders may not have one hand, arm or shoulder fixed on the ball carrier while attempting **to deflag him.**
http://www.tabramossportscenter.com/rules/flag_football_rule...




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Note added at 1 hr (2007-09-08 15:47:41 GMT)
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...to pulling the flag off the opponent. (I don't really need two prepositions for that ;-)

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Note added at 1 day13 mins (2007-09-09 14:46:55 GMT) Post-grading
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okay :-)