This applies to college football:

I noticed this in an early game last year, and I've wondered why no team takes advantage of it.

Here IT is:
After a running play that has been stopped in bounds, the clock keeps running, right? Well, if the offensive team comits a false start, they are penalized 5 yds, the 25 sec clock is restarted, and the game clock is restarted. So, you can run at least 49 secs off of the clock without snapping the ball. I dont' know if you could do this infinitely. If you can, then theoretically, you could end the game at a 0-0 tie without ever giving the ball to the opposing teams offense. I know that would never happen, but at the end of a game when you are winning, why not run out the clock by jumping off-sides when there is 1-2 secs left on the play clock.

Do you follow me?? Is there a rule about this??

Under NCAA rule we can start or stop the clock when 1 team is using obviously unfair tactics, which this would be.

A good rule of thumb I've been told is to not restart after a 2nd consecutive delay of game ... just in case the cause of the delay is simply to run off clock.

Staring-Stopping the Clock
 

In FN rules (3-6-3) When a team attemps to conserve or consume time illegally the referee shall order the clock started or stopped.

I would simply start the clock on the snap if a team tried this.

I would also get word to the coach via the wings to knock it off.

NF rule
 

Lets all be sure of this. In NF, 3-4-3 the clock shall start with the snap or when any free kick is touched other than first touching by K if the clock was stopped because:
(i) the penality for delay of game is accepted.

In the case of the false starts, after the second, I would send word to sidelines, use 3-6-3 and start clock on snap.

We're using NCAA here, but I didn't mean "Delay of Game" and shouldn't have typed that. I meant that to include any consecutive fouls blown before the snap. My bad.

Those tactics would be delay of game as the team is attempting to use the clock to gain an unfair advantage.

NCAA or NFHS empowers the referee to use whatever remedy necessary to prevent the team from making a travesty of the game.