How should I read "the 4 X 100 meter relay"?
The four times one hundred meter relay?
Or just 'the sprint relay'. There was a time when there was a '4 by 100 yard relay', but that was long ago (even before my youth).
PS On the question of 'Freestyle'. I think the choice of styles is free (at least, it was when I won a very slow 'Freestyle' race at school, swimming Breast Stroke), though understandably people choose the fastest stroke, which is Front Crawl. The thing about Front Crawl is that there are rules about technical things (like breathing, ankle-position [no 'screw kick'], number of foot beats per arm stroke... [I don't know the details]). 'Freestyle' is less inhibited by this sort of rule; in a 25m pool, some swimmers - for example - only breathe at the turns).