I'm sorry that I have very little of substance to add, but I wanted to say that I too have noticed this. It is very commonplace in sports reporting/broadcasting.

There seems to be quite a lot of fluidity on the use of prepositions in English. In my experience, prepositions are one of the more difficult aspects of mastering many languages. Word-for-word translations often use the wrong preposition.

To my mind, "on the day" sounds slightly more formal than "for the day," but perhaps that is simply the context (a report, albeit a sports report) in which it is so often used.

I was transplanted here in southern Iowa more than two decades ago from regions only slightly north of here (also within Iowa) where I spent another couple decades before that. I am still amazed at the differences that exist in language and culture barely an hour south of the land of my origin. I sometimes feel as though I've been dropped into the Deep South.

As a result of living in this rural area, I have picked up a number of (what seem to me like) southern expressions and usages. In my previous life, I don't remember ever hearing or using the verb "to fetch" (except in Jack and Jill); nowadays, however, I use it almost exclusively in place of "to get and bring back". No one seems to think a thing of it -- probably because they all use it too.

To my mind there are absolutely no inherent negative connotations to using "fetch" in place of "go get". Sure, it could be said in an offensive way, just as "go get" could. But if a person were to take offense at merely being innocently asked to "fetch" someone or something, we would all chuckle to ourselves and probably realize they come from a region where "fetch" is only used as a canine command.

It is something akin to "lit" and "of an evening" -- a pair of words/phrases that I had not experienced until I moved here. If someone slips on the ice here in Southern Iowa it is not uncommon to hear them say they "lit on their backside." If I'm trying to set an appointment with a person who works during the day, they might suggest I try paying them a visit "of an evening." Both of these seem regional to me. So does the use of "fetch" in place of "go get".