I think that their coach is the bigger issue. She is not playing and need not be dressed that way.
As for the girls, I think that the clothes might be as modest as you can get while playing the sport. As far as girls' sports, if they are in a closed venue with a known girls sport taking place, then if some guy shows up there and finds himself "tempted," then he should have known better than to go there. But it looks like they are outside of the sports venue, and the picture should not have been taken that way. They could have had them stand up and capture only the view above the bottoms of their uniforms. So, for instance, if there's a private property, a camp, for instance, where it's just girls in attendance, they could go swimming. So what might be OK in that context, may not be outside of it. Same thing applies to some girls' sports. In a Catholic society, girls' sporting events should likely be offlimits to men and boys ... except as necessary. But, as it is, if they restrict their immodesty to within the venue, nobody is forcing any man to attend. If I walk into a womens' locker room and see nude women, is that their fault and are they being "immodest"? I should not have gone in there ... obviously. Likewise, if there's a girls' swim meet, I should not go in there, nor a girls' volleyball game.
So, the rules, IMO, should be:
1) dress as modestly as possible given the sport if someone is playing (coach and other staff do not count)
2) keep the objectively-immodest dress within the venue (don't venture outside of the venue or take pictures that aren't properly cropped)