Sounds like that team is out for blood and wanting to win badly. Technically they can make you forfeit for not having a legal line up at the start, unless you have a league rule that says otherwise. With that being said I can't ever remember making a team forfeit for being late in all the leagues that I have bowled in over the years.
Yea. I've been in a league like that and have had to forfeit a game because the rest of the team was late. If you don't like the rule try to get it changed next season. We had to put it in cause one team was always late. I think we had until the third frame to catch up of else it was a forfeit.