This threw me for a loop at first, too. Then I had to reread it. It says that the *challenges* were upheld. In other words, managers believed that he made the wrong call; so , they challenged the call. And their challenges were upheld, with Ángel’s calls being overturned.
"...from 2016 to 2018 a whopping 78% of challenges to Ángel’s calls at first base were upheld."
Huh? You mean overturned, not upheld? Held up? Who's on first?
This threw me for a loop at first, too. Then I had to reread it. It says that the *challenges* were upheld. In other words, managers believed that he made the wrong call; so , they challenged the call. And their challenges were upheld, with Ángel’s calls being overturned.
Ahhh, I see now, thanks!