After looking at my 1948-'49 Leaf baseball page, Cheryl writes:
"I found a Kenny Washington Leaf Gum Co. All Star Football Gum card in an old book. Copyright 1948. I don't see it on the list of cards for this set and was wondering what set it belonged to. Kenny is wearing a blue jersey with #39 with orange back drop and yellow stripe with black lettering. Back of card says 17-Kenny Washington.
Just curious to find out more about the set."
(Image from Dave's Vintage Football Cards...a great seller)
In addition to their baseball set, Leaf issued similar-looking sets in 1948 for football and boxing. A second football set was released in 1949 before Leaf stopped making cards. Your Kenny Washington card is from the 1948 Leaf football set and in average condition is worth about $10-15. There are 98 cards in the set (just like the 1948/49 baseball set, only there is no number-skipping in the football set) and the last 49 are much rarer than the first 49.
The seller whose website provided the image above has several cards from the set available. Interestingly, Kenny Washington's card isn't one of them. In any case, click the link above and check out what he has.
Despite issues with color registration and notoriously bad centering, I like the 1948 and '49 Leaf sets. They look terrific when the colors are aligned properly, although I don't mind when they're not.