ah that makes sense - I was thinking of the defending team being whoever was not in possession of the ball.
I could tell.
Every team is defending their goal line at all times, whether, at any given moment, they are the offensive team, or the defensive team.
A player of a either team - whether his team is the offensive team or the defensive team at any moment - can provide the impetus that causes the ball to become dead behind either goal line. In the given example, a Team A player - on defense at that moment - imparted the impetus that caused the ball to travel from the field of play across B's goal line and out of bounds. (Note that Team B was still in team possession at that moment, so they were on offense, even though the ball was loose). No different than a kickoff or a punt that becomes dead in, or goes OB at, the opponent's end zone, the result is a touchback.
One of the biggest problems for newer officials is learning to stop looking at the game like a player or a coach (or a spectator). When a team intercepts a pass and is returning the ball, the players, coaches, and most spectators of the intercepting team still see their players as "defense," even though they are now, officially, on offense. I don't say that to be insulting or disparaging to those folks, only to point out that we, as officials, have to see and think from a pure rules perspective, and recognize which team is on offense and which team is on defense at any given moment during a down. I know I'm being patronizing, here (please forgive me), but that's the whole point of the rules using 'Team A' and 'Team B' to designate the teams, rather than 'offense' or 'defense.' As a referee, we have to be able to recognize that fact, very much in real time, when we are making penalty announcements, when there has been a change of team possession during the down. In those cases, we shouldn't use 'offense' or 'defense.' Rather, we should use, 'passing team,' 'fumbling team, 'return team,' 'Michigan State,' etc. (Never use a team color or mascot name. NEVER.) In the given example, Team A was the defense at the time of the foul. If you announced them as the 'defense,' you would be absolutely correct, officially, but you would confuse everybody except the other guys on your crew. In this case, you would really need to use the team names, like, "Illegal batting; number 89; Texas A&M. That's a 10-yard penalty; first down; Washington State." In this specific case, everybody (except your crew) will still be confused, but there is nothing you can do about that, without getting into an impromptu rules seminar. But, if you can think to add a short explanation of the result of the down, it could help with credibility. Like:
"The ball was batted by Texas A&M across Washington States's goal line and out of bounds; therefore, the result of the down is a touchback. The batting of the ball by number 89, Texas A&M, was illegal. That's a 10-yard penalty; first down; Washington State."
Thanks for giving me an opportunity to waste some time at work this morning.
