When does headshots greater than 100% occur in legal play?

On the NAMC (classic) server, I see a lot of low-levels with headshots > 100%. I have become unfamilar with the nuances of Standard mode play-- and all of these guys have dogtags....

Do I recall that Orbitals, explosives, or somesuch could cause this? Many of these players show no other hard evidence of cheating and/or have otherwise un-noteworthy stats.

..... so I'm askin'.