Basketball Official here trying to get a rule and reasoning behind a play I saw last night.

A buddy of mine was doing a big H.S. Varsity football game last night, so I thought I would go and check it out.

Buddy was the visiting side linesman.
The visiting team was on defense. The defense only had 10 players on the field...so a visiting team player ran out on the field to make it eleven.
The only problem was that when the player left the sideline, he was now on the offensive side of the ball. It was close, but in my buddy's judgement (and mine) the player did not get across the line of scrimmage before the offensive team snapped the ball. Thus, a defensiive player was on the wrong side of the ball, even though he was running toward the defensive side.
Buddy threw a flag...discussion with Referee...picked up flag.
Why?

I don't have my books with me RookieDude, but defensive substitutes are not considered players until they get onto their own side of the line as far as Encroachment penalties go. I would think however you potentially have an illegal substitution, and possibly illegal participation. I would be interested to hear what your buddy says about the discussion with the White hat.

Illegal Substitution
 

Should have been live ball illegal substitution foul. I don't think you'd have IP here.

NFHS Rule 3-7-6
An entering substitute shall be on his team's side of the neutral zone when the ball is snapped or free kicked.

REPLY: cmathews has it correct...It would either be illegal substitution if he didn't make it to his side of the neutral zone prior to the snap, or it could turn into illegal participation if he chose to do something prior to making it there (block, attempt a tackle, even if he drew coverage by the offense). The only reason I could see for picking up the flag would be if they jointly decided that he had made it to his side of the NZ prior to the snap.

Maybe the R just overuled him.

The conversation could possibly have gone like this:

R - Are you sure he was on the wrong side of the line?
L - It was close.
R - Let's wave it off.

Another possibility - what was the score?

Some of the officials went out for a brown pop after the game...that's where I asked my buddy why they picked up the flag. (R didn't go to the establishment)
He said something about the R saying the player wasn't a legal participant untill he got to the other side of the line of scrimmage.
My buddy might have been overruled as previously stated...as for the game...winner goes to the playoffs, loser is out for the season.
Score at the time was 21(Home) 7(Visitor) late in the 3rd quarter.
Home team ended up winning 21-7.

The R was wrong. If he said the guy was not on his side of the NZ, ill substitution, and if he participates it is illegal participation, which is 15 yards. (casebook illegal participation # 5) Now at the time and score of that game, go with the ill participation if needed, but if blowout he was on his side and no foul.

I have a question about this particular situation. Does the foul for the defensive substitute not getting to his side of the neutral zone (illegal substitution, 5 yds, simultaneous with the snap) automatically become illegal participation if this player participates in the play? Or is it a seperate foul with a second flag at the spot of participation with options for the offended team? The reason I ask is this. Game situation is this 3rd and 4 at the 50. B1 potential substitute does not get to his side of the neutral zone before the snap. A sweeps away from him and B1 doesn't participate or follow the play. A gets stuffed at the line and retreats and reverses the play back toward B1. B1 now makes the tackle 15 yards behind the line of scrimmage. If we have a seperate foul for illegal substitution simultanious with the snap, A could choose that option and have a 1st and 10 at B's 45. If we don't have a seperate penalty and you determine B1's participation occured at the spot of the tackle we now penalize 15 yards from the end of the run and we have 3rd and 4 from the 50. I am curious how everyone would handle this situation.

Great question! You are exactly right in needing 2 flags on the play. The illegal substitution is a foul simultaneous with the snap, 5 yards PS, and if he then influences the play or touches the ball, it becomes a live ball illegal participation foul. Illegal participation is a foul at the spot of the infraction and is penalized by the all but one principle. It would be tacked on if a running play, and 15 from PS if a loose ball play.
This exact senario is in the casebook ill part # 5 on page 73.

The R said he was not a legal participant? Then I guess that also means he was illegal, huh? If not influencing the play, then we have IS. Unless it's a blowout late, I'd have to go with IS.

I'm not really big on picking up a flag simply because of the score. If you don't want to enforce something because of the score, don't throw the flag.