I think there is a difference between how sports fans feel about LGBT+ people, and how the people in charge of the league organisations feel. Stonewall's research appears to have been looking at the former, while the latter are the ones who make the rules. That said, if the research is correct and sports fans are genuinely supportive of trans athletes, then they should be pressuring the league organisations to stop discriminating against them.
If excluding trans folk wasn't broadly tolerated by sports fans, it wouldn't be so widespread.
I think the more likely scenario is that the work focused on LGBTQ folks as a whole and simply didn't look at the very divergent experiences of trans folk in sports. Not mentioning that limitation is a strange oversight from pink news
Presumably provided that they're with the correct team. I'm sure lgbtq fans and members of the opposing team is hated just as much as the cis/straight equivalent, which I guess is equality.