They saw how Sunset can run fast that leads CHS to a massive victory againt Crystal Prep in soccer, it was technically her horse speed since she was from Equestria. So basically, she's still this fast, even when she's a human in her current home.
So, Applejack challenged Sunset to see if she's faster than any of the horses at her stable.
But we can't forget who always been the fastest person in the group.
If shes as fast as a horse does that mean shes as strong as horse too?
10651152
Hmm. Didn't think of that, but the best answer to that is to answer our own interpretations.
This reminds me of an idea I had a while back. Why hasn't anyone written an EG/MLP fanfic based on Uma Musume Pretty Derby?
10651248
I was just thinking that when I was reading this.
10651248
Im to this day still curious if someone will make it, I mean season 2 is out and the game too. Which I found the game to be quite enjoyable
10728442
They made a game for it???
107286
Yeah originally made the anime for the game, but it way delayed until this year
10729289
If you two are going to talk, then try to converse with each other through PM
Sorry if I sound mean
Sunset: Even though you cheated using your power you hypocrite.
Rainbow: Touché.
Rainbow's speed has nothing to do with Sunset's and doesn't affect it one iota so that line makes no sense.