Verified maple leaves brown
Your maple ran short of water, most likely during a recent heat wave. Even if the soil may have been adequately moist at the time, the roots weren’t able to supply water fast enough to meet the top’s demands.
When you examine the damaged portion, you’ll realize that the tissue is paper-thin, fragile, and will crush easily. The brown spots will remain until the leaves drop later in the year. It’s very possible that the sunny side of the tree has more severe damage than the shaded side.