Played a ton of sports and the most serious was a broken pinky finger from a catch in cold weather game.
Extremely lucky. I’ve played in multiple games where dudes got their necks broken.
Yeah the bold is probably the more interesting question as I've been similarly fortunate to avoid major injuries but for the couple I mentioned above despite playing hundreds of hours of contact sports.
Significant injuries I've witnessed:
I've twice seen a guy's tibia sticking out of his leg. Once was soccer when I was playing in a club tournament ~12 years old. My teammate, playing midfield (he was our best player), pushed the ball forward around midfield. I was maybe ten yards ahead of him (I was playing striker) and tried to get wide and parallel to the last defender. While doing so two defenders converged on my teammate and slide tackled him hard, including one sliding at his shin. I still remember the snap and my teammate's scream and everybody getting really quiet (except for him) when we saw his bone sticking out. Ambulance had to come onto the field and I think we withdraw from the tournament. I don't believe I ever saw the kid again.
Similarly, while playing pickup basketball with some former high school classmates around 19-20 my friend/teammate and I got on a fast break. This particular court - which was inside of a batting cage/arcade type place - had a chain link fence not far behind the hoop. Teammate went up for the layup a bit out of control and must have landed at like the base of the defense. I didn't see it initially but I can still quite audibly hear the snap of his tibia - which at the immediate time I just thought was the fence. He actually didn't initially scream but he saw my facial reaction when I looked down at his bone sticking out of his shin. He then started screaming. I believe he was on crutches for at least a year.
Playing in the ASA national slowpitch softball tournament in 2010 I watched a runner on third (there were no "safety" leads from third allowed in ASA at that time) take a line drive to the head and drop immediately. He later died at the hospital.
I've seen several guys blow out their knees at various times in various sports. Worst was my amateur baseball teammate's knee seemingly explode when he crossed home plate awkwardly in wet conditions (basically his metal cleats slide a but across the plate when all his weight was on that leg). He never played again.