They are low because the police don't have the resources to nick them.
Here's an example from my own personal experience last week.
I was pressured into working a train full of fans who had trashed the previous train which was cancelled. Even though they witnessed it they "Couldn't identify the culprits and just want them gone."
They wouldn't allow any officers to travel with me to their main destination as they "We're allocated elsewhere..."
After the driver and I refused we finally got the officers to travel.
On board, as well as getting off they were fighting and abusing myself and the police at stations. One threatened me. I asked the police to remove him. They had a 'chat' and put back him on the train. Only telling me once they all fucked off at Stoke.
There's a minority of dickheads in all football club who cannot or, won't behave in public. They don't feel the need to act decent in a public setting. I'm all for identifying them.
However, the spray idea doesn't work for me. As I have to deal with them on a weekly during the season. What happens if I'm accidentally sprayed and a few months late I'm hauled away because it's on me when I'm travelling to a game?