Look round the other local clubs and ask parents if you can find out who plays where. Did the coach explain why he was dropped and if it was a temporary measure or could he come back in the summer? Speak to the Club Welfare Officer to get an understanding of the club's policy on how teams are selected and exclusion from training.
Unless there is a clear selection policy or restriction on numbers which should usually be based on first come first served, it is unusual for a club to drop 6 year olds from training. It is sadly common for kids to be left off the team sheet or left sitting on the bench or to be otherwise excluded so they leave of their own accord.
However, there are many clubs, often run by volunteers and parents who are more inclusive.
I am not English so cricket always seems a bit tough on weaker players who sit around all day waiting for their turn to bat which might not even happen if the batting order never gets that far.
Children should try as many sports as they can before the age of 10 so maybe look at summer camps for hockey, cricket and rugby before signing up for next year.
My eldest was small and a bit slow so often left on the side of the pitch. He desperately wanted to play football but actually hated the experience. He started hockey and he is really really good. Lovely team!! He also tried rugby (I was terrified as he is quite small) and cricket which he loves but we are in an area where they don't play much and he has kind of left it a bit late to start.. he was 13 when he started.
He still played football at school for a while and now plays with his mates alot, as well as the students and teachers at his school on Friday afternoons, it is a good skill to have as it is how lots of boys bond but not exclusively of course.
My youngest LOVES football as do a lot of his close friends, some of whom are seriously good, international club tournaments at age 10. Most of his group of kids play for different local teams and find one that suits their level. We are in an area where there are probably 4 clubs to choose from all with between 3 and 6 teams at each age group. My son is looking to move this year which is proving difficult as some of the clubs are less friendly and welcoming than others.
I hope you find somewhere he can have fun!! Our hockey club motto is 'A club where I belong'