Per the wiki's Tag:natural=sand page:
"This [natural=sand] tag should not be used for the infields of baseball or softball fields (a form of tagging for the renderer) - use surface=dirt instead."

I understand that baseball fields look prettier when rendered on OSM, Mapbox, etc, but it is important to adhere to the wiki, especially in explicit cases such as these. Fun fact: the infield mix college pitches usually use is only about 60% actual sand.