What causes this green trail?

https://www.legacysurvey.org//viewer/?ra=19.8996&dec=0.1285&layer=hsc-dr2&zoom=14&hsc-dr2-cosmos

Is it possible that it’s a comet?

I don’t have dates for the individual exposures that make up HSC-DR2, so I can’t provide the JPL Horizons lookup…

Certainly looks like a comet to me.