Is B1 not still moving forward, towards A1, after A1 jumped?

Glad to see the official used the correct signal on the throw-in violation.

I like both calls.

However, the throw-in should have been from the C's side of the key - the opposite side from where the ball was inbounded.

Looks to me like B1 is straightening his body and not moving towards A1.

I watched it live, and thought it was a block, as I thought the defender was moving towards the offensive player when the contact occurred. The replays I saw did nothing to dissuade me of my notion. (and no, I'm not a Minnesota homer).

The throw-in violation surprised the hell out of me when it happened, in a "did he really just do that?" kind of way.

Left heel was over RA arc, block.

Last night, observing BV game, 3-man crew endline spot throw-in, thrower leaves the spot, but the only official that realized it to be a violation was the Trail. He chose not to come in on the call.
After the game I asked him about it, and he admitted having second thoughts, but didn't want to "take over the game," by coming in on his partner.
Thoughts, comments, please.

I think he should have made the call. The other night I had a first in 30 yrs. calling a backcourt violation from the lead position: Missed attempt bounced to the corner where on offensive player ran it down and before going OOB threw the ball into the backcourt where a teammate retrieved it. Waited a sec. to see if T or C recognized it and when they didn't, man, I just "took over that game" and made the call.

I had the same situation about 15 years ago in a BV game. I was the new L on a backcourt inbounds play after a time out. A1 left the designated spot along the end line and I came in and called the violation when the new T brain locked and the C didn't pick it up, either. I felt awkward for a moment coming in from 50 feet away but the three of us had gotten together during the TO (it was late in the game) and reminded each other that it was a spot throw-in. I would've felt worse letting the play continue.

Yep - he is clearly outside the 3 ft space. Just for my understanding though, isn't it true that the thrower does not have to be completely inside the 3ft space - just as long as part of him/her (a foot) is in the 3ft space?

Correct -- in or over the space

We had one last night, FC throw on the end line. I'm C. Thrower starts to slide over under the basket, slowly, and eventually gets to about half-way through the lane before he throws the ball in. I debated making the call, but he would have had to get further before I called it.

L admitted later that he should have called it.

hahaha :D