Who says you can't use a suit jacket as a sports coat? The suit below was meant to be used this way. The "no suit jacket as sports coat" rule is a modern creation and should be taken with a grain of salt.
Note the pinched front that was a short-lived fad for the youth in the late 1930s and early 1940s and the patch pockets. Also interesting is the shoulder gusset (bi-swing back) lacking a belted back, the two being rather commonly combined during this time period. Four button jacket instead of six like your grandpa's suit.
Also take note of the shipping weight: 5 pounds for a two piece suit. Modern material density and weight (along with the quality) have fallen far from the tree.
click photos to enlarge
Look, another bi-swing back that lacks the belted back. A neat sports coat in the truest sense of the word. Note the green again.
A couple of great collegiate looks for the young beau.