All leagues have a restriction on the number of individual swims you can do, normally two.  It might be that your ‘best’ stroke is say freestyle, but you’re also the fastest at the other strokes too.  The gap between times might be nearest on freestyle and therefore the alternate swimmer is selected here.  We will also try to mix up swims to allow swimmers to compete across different events.  No junior swimmer should be labelling themselves as a particular expert in any one stroke.  There’s also the matter of Butterfly.  No one really wants/likes it, but someone has to do it!