Here's something I don't think a lot of people know.
Daisy's sports outfit is unique to her and is technically her main outfit! Explanation below.
Daisy would fit in Smash way better in her sports clothing and it would make more sense. Before you say "No, she'd be wearing her dress," well Wario wears his biker clothing. Sure, it's because he is representing his WarioWare inc series, but then again, so would Daisy. She'd mostly use sports attacks and represent the Mario sports, games, which she only appears in her sports outfit. Daisy is only in her dress in Mario Party and Mario Kart as well as a few minor games like Fortune Street. Every other game, she is literally in her sports outfit. Even if you check MarioWiki, it tells you that a majority of Daisy's appearances are in her sports clothes, and there are less games with her in the dress. Thus, she'd wear her sports outfit to represent the sports games and her sporty moves, and also because it's the outfit she wears for a majority of the time.
And before people say "Daisy's sports outfit isn't unique to her, since Peach has the same one, too!"
Actually, it
is unique to her, separate from Peach. The very first sports game with the princesses' current designs (Mario Golf Toadstool Tour) features Peach in her skirt, and Daisy in her booty shorts. Peach had worn a skirt while Daisy wore the booty shorts. This same instance also happened in Mario Power Tennis. Sadly in newer games they gave Peach shorts just like Daisy, and in even more recent games they give them both skirts. But if you think about it, Daisy is the original wearer of the sports outfit with shorts, so it's unique to her. I wish they would continue to use the Peach skirt and Daisy short contrast in future games instead of giving them the same outfit in the same game.
My hope for Mario Tennis Ultra Smash is that Daisy will wear shorts, not the skirt, since Peach had already been shown wearing the skirt in previews. Sadly, in the upcoming Mario and Sonic Rio 2016 game promo, Peach is shown in her sports shorts...
This is probably my least favorite of Peach's outfits, as it makes her wear the same thing as Daisy. I like the skirt on her better, while Daisy looks nicer to me in the shorts.