Generally speaking, on a descent, everyone is on their own. Some riders like to tuck and bomb descents, others like to sit up and coast. Most are somewhere in between. Just like cars on a multilane highway, slower traffic should stay to the right. Faster traffic passes on the left.

It sounds like your group was trying to run a paceline down a descent, which is hard to do, because on a descent, most riders will naturally back off the rider ahead of them to add space for maneuvering as the speed increases. The paceline will stretch out and it won't really be a paceline anymore.

By my interpretation, it makes sense that rider A, whose shift at the front was probably up, pulled off as the descent began. I think that was a mistake. Rider A should have stayed where they were and let whoever wanted to go faster pass them on the left. By pulling off and closing down the passing lane, rider A has prevented anyone else from coming out and riding the descent at a different speed. That's why rider B eventually has to go around rider A.

I'm sure all rider A was thinking was that my shift is done, I'm tired, and I'm pulling off. Yes, but not on a descent. Stay where you are, let the faster riders go around you, and when the paceline reforms at the bottom, grab the back position.

Generally speaking, on a descent, everyone is on their own. Some riders like to tuck and bomb descents, others like to sit up and coast. Most are somewhere in between. Just like cars on a multilane highway, slower traffic should stay to the right. Faster traffic passes on the left.

It sounds like your group was trying to run a paceline down a descent, which is hard to do, because on a descent, most riders will naturally back off the rider ahead of them to add space for maneuvering as the speed increases. The paceline will stretch out and it won't really be a paceline anymore.

By my interpretation, it makes sense that rider A, whose shift at the front was probably up, pulled off as the descent began. I think that was a mistake. Rider A should have stayed where they were and let whoever wanted to go faster pass them on the left. By pulling off and closing down the passing lane, rider A has prevented anyone else from coming out and riding the descent at a different speed. That's why rider B eventually has to go around rider A.

I'm sure all rider A was thinking was that my shift is done, I'm tired, and I'm pulling off. Yes, but not when you are starting a descent. Once you start going downhill, it will take less effort to maintain your current speed, so you can ease up a bit. If the road is steep enough, you can even coast, as long as you don't slow down. The pack behind is doing the same, so stay where you are and let the situation sort itself out. Riders who want to go faster will pass you. Riders who don't will stay behind. Enjoy the descent, and when the paceline reforms at the bottom, grab the back position.