Hi,
https://www.openstreetmap.org/relation/19345794 does not look like a horse riding arena (leisure=pitch + sport=equestrian) and https://www.openstreetmap.org/way/1412930874 does not look like an equestrian centre; the whole thing is probably this small racecourse: http://murotaht.web.fc2.com/
Compare
https://wiki.openstreetmap.org/wiki/How_to_map_a#Racecourse_(horse_racing)
https://www.openstreetmap.org/way/571204779 (example)