Leaves falling off of tree in late spring/early summer
The tree looks like a type of maple and they can overproduce leaves. This looks like some leaf spots on the leaves such as anthracnose and phyllosticta.
The heavy rains and frequent cloud cover over the last couple of weeks makes plants susceptible. You may see some defoliation during high infection periods.
These leaf diseases on mature trees will not be a major problem threatening the health of the tree. No control is necessary. The best management practices involve pruning and removal of dead twigs during the winter or dry summer months. Mature trees can be thinned for better air circulation throughout the canopy. Rake and remove infected fallen leaves in the fall. http://extension.umd.edu/hgic/shade-tree-anthracnose-trees