I played competitive ultimate in undergrad and grad school, then played and traveled on club teams for several years before my first ACL tear six years ago at age 27. Tear happened in a practice scrimmage, not even in a real game.
ACL repair, followed by months of rehab and about a year break from playing, and I eventually started again. Carefully using an ACL sports brace (big, serious thing) for about two years before finally feeling confident enough to downsize to a neoprene brace. For those four years, I wasn't playing with a traveling club team -- just playing in the competitive local leagues, and helping coach/captain some less experienced teams. Then a little over a year ago, an end-zone collision in a low-key summer season game tore the ACL-repair (same knee), and sent me back to the surgeon for another ACL-repair; I'm now 11-months post-surgery, and still nowhere close to where I was before the second injury.
From what I've learned, you basically have three strikes. There are three ways to "repair" a town ACL, and you can only do each one once. None of them works as well as your original ACL, so with each surgery, it ups your odds of reinjury.
Having played years of competitive ultimate, I'd guess the majority of serious players have suffered at least one ACL-injury. Many have suffered more than one.
For me, two-surgeries on the same knee means it's time to quit, no matter how much I want to play. If it happens again, that's pretty much the last strike. After three surgeries, any additional injury and your options become knee-replacement, or living without an ACL. Neither one is a good option.
However, in support of people playing one of my favorite sports, I'd recommend that if you do play, be VERY CAREFUL in your choice of footwear. Both injuries happened on landing from a jump when wearing very grippy soccer cleats on soft grass. When jumping for a Frisbee, usually one of your legs lands first, and that absorbs all of your force. If the ground is soft (but not muddy), then you have unbelievable traction. The cleats press straight into the ground, and then your leg/knee is anchored like it's in concrete. Any lateral force that twists that knee is absorbed by the ACL, and that is far more force than an ACL can absorb. When the foot can't twist or slip, then the ACL takes all the lateral force, and it's going to snap. It's like anchoring a baseball bat to a dime-store rubber band and asking McGuire to swing for the fences. The rubber band isn't going to hold back the swing -- it's going to snap.
If I had it to do over -- or were coaching a team -- I'd strongly recommend players bringing several pairs of shoes to swap out based on field conditions. The goal on the field is traction, but too much traction becomes dangerous. On soft fields, I'd recommend less aggressive cleats for safety reasons. It's better to slip occasionally than it is to lose a knee.
That said, disc golf and ultimate have very few things in common other than the fact that both involve throwing discs through the air. They have about as much in common as soccer does to golf -- sure, both involve propelling round objects toward a target, but that's where the similarities end.
Still wondering if there are any disc golfers here -- the similarities between disc golf and hiking are actually a lot closer than the similarities between disc golf and Ultimate. In disc golf -- at least with the best courses -- you spend most of your time hiking through beautiful trees and hills. It's a way to spice up a beautiful walk and to enjoy nature either by yourself or with a few close friends. Disc golf and hiking are definitely compatible passions.