Jumping in is usually a brutal practice. As well as trampling the less pushy, it means that anyone singing or playing as a duo, trio or more has next to no chance of getting started.

If there was a group understanding that no-one should claim more than a single turn before everyone in the room has had a bash it might be a bit more equitable, but it's more likely that the group will behave like a shoal of piranah going after a lone paddler.

Valmai (Lewes)