Amtgard was apparently cobbled together from Dagorhir and Eamangarth by a con artist in the 1980's. True story.
Yep!
Over time, the fighting styles have evolved differently due to different rules.
For example, in Belegarth/Dagorhir, shield bashing and grappling are very much allowed. AFAIK, in Amtgard, this is a no-no. As a result, Bel/Dag combat has grown much more in-your-face. There's a lot more knock-them-on-the-ground-then-kill-them going on.
Also, flails in Dag/Bel need a big head and a short chain. Not so in Amtgard, where you at least used to have (and still might have) these crazy-ass long chain things.
In Dag/Bel, you are expected to land blows with some degree of force. If your shot is legitimately light, it can and will be called off. By the same token, dag/bel has weight
minimums for weapons - so Amtgard's kite-spar + pipe insulation + nylon stocking weapons won't pass. And, again, it requires different fighting styles.
Amtgard lets you attach weapons to shields, so madu are popular. There are construction requirements for weapons and shields in dag/bel which make these impossible.
There are some excellent fighters in both sports. The best of the best in Amtgard tend to be very, very fast. The best of the best in Dag/Bel tend to be very strong. In both cases, they're pretty excellent athletes.
I visited an Amtgard practice in Tucson way back when. I participated in their "ditching" which is basically like every fight in Belegarth - no magic, no characters, just combat. It was fun and remarkably similar.
-O