Battery Acid Spill

[Champa]

What would cause the battery fluid to spill? I checked under the hood recently and saw that some battery fluid had spilled. I noticed since the retaining clip was rusting and the paint around the fenderwell was damaged. I flushed enough water through there, and I am going to spread some baking soda too. I didn't go offroading or anything, perhaps one or two hard brakes perhaps, but I wouldn't expect that to cause the battery to spill.

Any ideas? Thanks