Work is not defined as something you get paid for. The bible is clear that even the cattle are to observe a day of complete rest; complete (Lev 23:32). Cattle don't get paid! Yet they were to rest to. Furthermore, the Bible says sabbath is to be kept holy. I think this means devoted to God, not to our hobbies. The Bible says one should not even cook on a sabbath let alone mow your grass.
I think that the phrase “devoted to God” is the key.
For instance, going along with curing the sick, serving in a soup kitchen on Sunday, providing the food and drink for fellowship after Mass, or even shoveling the walk up to church before Mass so that the people can make it it is certainly not against God’s law.