NBC had a string of live-action failures as well as animated ones in the mid-70's. While Land of the Lost lasted three seasons, and Run, Joe, Run got two, everything else seemed to be one and done.
The network had tried out an anthology series that was more educational than entertaining, called GO!, styled more in the vein of CBS' You Are There, but in 1976, what was originally titled GO!-City, as demonstrated in a bumper you'll see in the following video, was renamed Muggsy, after the title character, a teenage girl who, with her brother as her only family/support, wanders through the city, and gets into all kinds of trouble.
Sure enough, Muggsy was a bomb, and that was because the network placed it in the lunch hour death zone, where few shows seem to succeed. CBS had gotten lucky with Fat Albert, which deserved an earlier time slot through its 12 seasons, but never got it.
70'sKidVid uploaded the open & close. As you'll see, the network itself produced the series, seeing as how the trio of Bill D'Angelo, R. S. Allen, & Harvey Bullock had given them nothing but failures other than the aforementioned Run, Joe, Run. If the singer's voice sounds familiar, it should. It's David Clayton Thomas of Blood, Sweat, & Tears.
No rating. Never saw the show.