Then that makes him an excellent example of having a career-ending injury.
I believe I said exactly that, in post #10. 
Few people recall that St. Louis Cardinals legend Stan Musial was originally signed as a pitcher. His record in the minor leagues was 33-13 before he fell on his shoulder, injuring it and ending his pitching career. While Musial would play 22 seasons in the majorsas a first baseman and outfielder, his throwing was only considered “marginal” or “adequate.”
In memory of Jack Tatum’s passing away today: He ended Darry Stingley’s career with a hit that caused quadriplegia. The only more severe “career-ending” injury than that might have to be Ray Chapman’s beaning death.
Herb Score was a hard throwing pitcher who got hit in the eye by a line drive off Gil Mcdougals bat. he tried a comeback after a year or so but it did not last.
Worst one I ever saw as it happened was Napoleon McCallum on MNF. As Dan Dierdorf says, “Don’t look at this if you don’t want to see it”. Nasty. His leg was in danger of being amputated for a while.
As others have said, a career ender varies by sport, position, and age. A recoverable injury might end the career of a player in the last stages of his career.
Neck injuries, catastrophic knee injuries and arm injuries for a pitcher are usually the ones that do it though, despite advances in sports medicine.
Although Joe Theismann is my mental image of the career-ending injury, I wanted to note that Bo Jackson’s injury precluded what was shaping up to be a fabulous career.
I saw him (on TV) for the first time in a game against the Seattle Seahawks. He was a rookie. Seattle had a lineback who at that time was held in high regard, Brian Bosworth. Here is a summary of that game from Bosworth’s Wikipedia page:
That doesn’t do it justice. I saw that 91-yard run. Bosworth read the play, knew a sweep was coming, and when Jackson went in motion, Bosworth (correctly) committed himself to run to the sideline. Jackson had farther to go to reach the sideline and turn the corner while moving past the line of scrimmage; Bosworth had only to run to the sideline, and he went all-out. Jackson accelerated so fast that he swept around the line before Bosworth got within fingertip range, and was gone downfield like he’d been shot out of a gun.
One of the best linebackers in the league had read the pplay, focused on the ballcarrier, and gone all-out for a tackle, and had had absolutely no chance of reaching Jackson. My first thought was, “how in the world is anyone going to contain this guy?”
Career-ending injury, it turns out.
When was Brian Bosworth ever one of the best linebackers in the league? I remember him mostly as a big-talking non-performer who didn’t stick around the league very long.
Jack Newton - Wikipedia Jack Newton was a pro golfer who walked into a spinning propeller of a Cesna plane. It took off his arm and did a few other things. His career came to a sudden halt.
Yeah, no argument with that assessment. But that’s hindsight – at the time of that run, the talking heads considered him hot stuff (maybe I should have put quotes around “best” in One of the best linebackers in the league), and that’s what my impression was based on. At least Jackson turned out to be pretty good for his short career, if not quite so untouchable as that play implied.
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Meh, that’s nothing – try watching footage of Clint Malarchuk’s injury! 
He’s the reason goalies wear neckguards. (It didn’t end his career, though – he was back out on the ice, oh maybe three months later?)
Do NOT look up the footage unless you have a stomach made of damascus steel. 
The New York Giants are more than likely facing a career-ending injury to their 3rd round pick this year, safety Chad Jones. Part of the reason he was drafted is because their #1 pick in the 2008 draft, safety Kenny Phillips, was knocked out of the first game last year with a career-threatening condition.
At this point, being a safety drafted in the first few rounds by the Giants is a career-threatening proposition. Here’s hoping the free agents fare better.