Sportkilts are very common, and they sponsor a lot of games so their name is out there. For competition they are perfect, it's literally what they were designed for.

That being said, I don't use mine for anything but kicking around the house. Currently I'll either wear my Utilikilts (especially if I am attending the games myself, as the pockets let me hold my valuables without interfering with my throws) or my Stillwater Standards.

I had the chance to handle one of the new Stillwater Thrifty kilts recently, and I intend to buy a couple just for Games kilts. As light or maybe even lighter than the Sportkilt, velcro fastenings, and a nicer look than the SK.

One thing to be wary of is getting tacky on a nice kilt. That stuff is impossible to remove from clothing if it gets rubbed in, so don't wear your tank. I have seen guys out there throwing in one, but I don't recommend it.

For underwear I will either wear boxer briefs or bike shorts under the kilt. Both provide adequate coverage though the bike shorts will allow you to change out of the kilt in public if necessary, where boxer briefs are a little revealing for that. Boxers are a little too flimsy to give good coverage I think, and tighty whiteys are just the worst invention the world has ever known.