Calligraphy on horseback! Now that would take some serious skill and practice. There’s a modern Fujimori Festival at the eponymous shrine, though I dare not lean too hard on auto-translation to proclaim a direct linkage. Still, “Shrine of the horses and learning” sounds about right. 
“藤森祭／天応元年／藤森神社 (Fujimori Festival/Every 10 Years/8th Century” from the Miyako Nenju Gyoji Gajo (Picture Album of the Annual Festivals in the Miyako), hand-painted on silk by Nakajima Soyo (1928) :: via Bibliodyssey
Mar 17, 2009, updated Mar 31, 2025