SCA fighting is not choreographed. What makes this possible is our armour standards and weaponry. The SCA Heavy Fighter's sword is essentially a club: it's a stick of rattan wrapped in fibre tape and duct tape, given a blade side (defined with electrical tape), often with a basket hilt although cross hilts are common. SCA Rapier Fighters use schlagers or reproduction rapiers.
Most reenactment groups also fight in unchoreographed combat. In some specific situations such as a display where sometimes a desired result is needed as part of a show, the final result is known but earlier parts of combat are unscripted.
To make a sword for SCA Heavy Combat, first get a stick of rattan. After getting your stick of rattan, cut it down to a nice size. A "standard length" for a sword is a length that enables you to swing it loosely back and forth by your side and the tip just barely touches the ground - but, of course, you can make it to whatever you feel comfortable with. Wrap your rattan in fibre tape, then a good few layers of duct tape. Decide which side feels comfy and which side would make a good blade side (there are various arguments about which way the blade should go, but in the end, it's UP TO YOU). Attach the hilt. You may also like to add a thrusting tip.
There is your new SCA sword!
All other SCA Heavy Combat weapons are basically a variant on this.