There is a penalty on the play.
The flag is red and green, so is their football uniform.
To indicate that he has seen a penalty committed by one or more of the players.
An assistant referee DOES NOT need a whistle. They need a uniform (shirt, shorts, socks) and an assistant referee flag. That's pretty much it... oh, and soccer cleats will probably help!
In the game of soccer, a buzzer flag is a flag attached to a buzzer worn by the assistant referee, which causes a receiver to buzz, warning the referee of the flag's use.
There is no flag on the dress uniform
If the flag was inadvertent, or the official determines that a foul should not have been called, the procedure is to pick up the flag and wave it back and forth, to indicate that the foul is "waved off."
Yes, when you are wearing a uniform, you salute the flag both indoors and outdoors.
Why would they challenge a call if no call was made? Once the referee makes a call, the coach can then throw the challenge flag (if it is challengeable...not all calls are).
They officiate by blowing the whistle when the play is dead, throwing the flag when there is a penalty, judging whether or not a play actually resulted in a score, etc.
In flag football their is a flag if you tackle.