Mechanics question from non-football guy
 

Was watching a game with a couple of fellow basketball refs the other night, and saw the mechanic where an official (more than one on a lot of plays) would hold an arm straight out with their fist clinched. We were guessing its some kind of signal to their partners, but have no clue what it means. Would any of you football guys explain?

Most likely they are indicating that whichever team they are responsible for counting has 11 players on the field.
If it's the guys on the line, they could be indicating whether the offensive player closest to them is either on or off the line.

What most non-officials don't realize is that standard mechanics call for each field official to specifically count the players, of either the offense or defense, prior to EACH play during the game. At least 2 officials will be counting either the offense or defense, and the extended arm, closed fist is a standard signal to your counterpart that you have counted the players and there are 11 on the field.

There are other signals to indicate less than 11, and when there is more than 11, standard procedure is to verify the count and if doing so, stop the clock and penalize the offending team with a dead ball Illegal Substitution 5 yard penalty, (rather than allowing the play to off where the offending team could then suffer a 15 yard live ball foul for Illegal Participation).

Another practice not recognized is that each field official independently keeps track of the number of the down before EACH play, and independently confirms their count with the Linesman. Should there be a discepancy in that count with any official, the clock should be stopped until the discrepancy can be can be checked and eliminated.

Thank for the info! We wondered if it had something to do with positioning of the offense on the line since we most commonly saw the Linesman (or Line Judge?) do this. Then we saw the umpire with that signal once and that got us to wondering.