Okay, I received an email about Hans-Peter Finn (from someone who has sent me several names).
I looked a little deeper, and there are several references in New Zealand Newspapers. Seems he was actually killed on March 30, 1920, at the "jockey's club racecourse", Devonport-Takapuna. I know nothing about the venue, but it was listed as a grass-track, and was home to horse, dog, and motorcycle racing. He is also listed on the grasstrackgb website remembrance page.
Finn was apparently hit by another rider, and suffered various injuries. He was 37, and is buried in the Waikumete Cemetery.