Legally, “Assault” is putting somebody in fear of immediate unlawful force (regardless if it happen or not) and “Battery” is using unlawful force against somebody. Though literally nobody, including the police and the media use the legal definitions very much and simply use the terms as they are commonly understood.
Naturally, it is common that the two come together quite a lot, so most time(s) people are a victim of Assault+Battery (or Assault + a more serious offence)
Meaning, for sure the offence in the video could qualify for both- ditto for deliberately or recklessly splashing people with puddles in your car.
In fact, I recall that under the Offences against the Persons Act, deliberately or recklessly infecting someone with a disease equally counts as an offence, though more of a grey area. ABH is “some harm more than trivial” and doesn’t have to be permanent so if the victim in the video were to be infected with a more than trivial disease of some sort as a result of the sh*t-spray, then I think hypothetically in some scenarios the farmer could even be guilty of ABH.
The cyclist is trespassing (we presume) but that’s a civil offence so not sure how much mitigation it would offer the farmer.