Yes they've been constantly attacked since the early days of the protest, from last year. There's a lot of footage online of it from November/December.
I am from Kerala, which is currently ruled by the communists. I see protesters getting lathi charged and water cannoned pretty much every month (pre covid). So, honestly I can't say the farmers were treated badly based on the image in the BBC article. I am not saying violence is good, but police were lathi charging people during the corona lockdowns also.