Maple tree disease
It is very difficult to diagnose plant diseases without seeing it first-hand, however it appears that this is a foliage disease called anthracnose. This is not overly harmful to the plant, but is rather unsightly. It typically occurs when you have a fairly wet spring conditions, or in combination with some other factor (frost damage). There is not a lot you can do about it. It is unlikely to be as severe in future years.