Maple Trees Getting Spots on Leaves
It looks like you've got either anthracnose or tar spot but I can't be sure from your photos. Here is the U of M's guide regarding "spots or blotches on leaves": http://www.extension.umn.edu/garden/diagnose/plant/deciduous/maple/leavesspots.html
I'm leaning more toward anthracnose.
The response for both is generally the same, thankfully.
Best practice is to clean up leaves that fall--now and in the autumn. Both are passed via decaying leaves from the year before.
If a tree is completely defoliated several years in a row, you can consider a fungicide but if this is the first year, I'd try getting rid of as many fallen leaves as possible and see what happens next year.
Many thanks for your help!