For a contact sport, it seems impractical to me. It can accidentally (or intentionally) get yanked. Do they have the collars just to be unique in team sports?

A gentleman's shirt always has a collar. Also cuffs. Seriously. Mark L.

A Gentleman's Game A Gentleman's Shirt

History, team colours. The SA jersey has always been green with a "gold" collar, if there is no collar then what would be gold

The shirts look much better with a collar. Without them, the shirts just look like T-shirts.

a gentleman's shirt always has a collar and well some rugby shirts have a collar and some do not have a collar, and yes a collared shirt does get yanked on now and then but it pretty much is on the preference of the team