If two players on the offensive line move improperly before the snap, is it two false start penalties, to be served on top of one another, or does it just go down as one false start?
Just one.
Is there any situation where two penalties are assessed on a single play?
Yes. Personal fouls can be assessed on top of some other violation, but IIRC the enforcement of the “punishment” will generally lie in favor of the steeper penalty.
Edit: Meaning if a five-yard penalty is assessed on a player, then a 15 yard penalty (personal foul) is assessed against that same player or another on the same team, the refs enforce the 15 yarder over the five yarder, they don’t combine them.
Strictly speaking, no. Sometimes, however, you’ll see two penalties enforced between plays. For example, say a defender hits the ball carrier after the play is over and draws a 15-yard penalty for unnecessary roughness. He then goes over to the referee, screams in his face, and jabs his finger in the officials chest. At this point he’ll be penalized an additional 15 yards for unsportsmanlike conduct (and also ejected), leading to a cumulative penalty of 30 yards.
However, if a team commits two or more penalties on a single play, their opponents have to choose which one to accept.
Doesn’t “dead ball” come into play? Like you can have one penalty during the play enforced, and a later “dead ball” penalty also enforced? And they could be on one team or both?
Sure.
For some penalties you might have a loss of down on top of walking off yardage. For example, intentional grounding is 10 yards plus loss of down.
Conversely, on the defense some penalties include yardage plus an automatic first down, holding for example. It’s 5 yards and an automatic first, regardless of how much was needed to reach the new downs marker.
These aren’t two penalties per se, but two forms of punishment for a single infraction.
And, I think, you can’t have two false start penalties on one play anyway: as soon as one lineman false starts, the play is instantly dead. You can’t commit a dead ball false start, so there’s no second penalty.
Though it is possible to have two other penalties on a single play (for example, two different instances of holding), so the explanations above about the defense picking one are relevant in those cases.
Think of it this way, breaking a procedure rule is singular and results in a dead play, it doesn’t matter how many players are involved.
On the other side of the ball, so is an offside penalty, it doesn’t matter how many players are offside but the fact that they are offside.