I don't collect sports cards for the most part, but i do like 1930s-1940s era sports like Goudey Sport Kings, and National Chicle's Football cards. At some point, when does sport become a non-sport card?

Eddie Rickenbacker as a race driver is technically a sports card, but is also historical now considering it's pre-WW1. Charles Lindbergh is another example. Sportsman then but basically historical now. There are also things like Amalgamted Press' Sports Queeriosities and Ripley's Believe it or Not cards which straddle the line at times.

Interesting question. My first reaction is when you want a card or set for a reason other than the sport, like when people started buying OJ Simpson cards. I have some old baseball cards specifically because of the historical significance of the player or their part in a historic game / team - like the 1989 world series / earthquake.

I think it can also be when the marketing of the set is not directly sports. I tend to think of any set with non-athletes as big draws as non-sport. Golden Age, Americana, Goudey, Allen & Ginter, etc all fall into this for me. I would not buy any of them for the sports figures, even though I love sports; but I buy them. Some of the recent mainstream "sports" have contained celebrity autos because they were fans. Those are non-sport for me.

I think all illustrated sports card sets (that is, when drawings or paintings used to depict the subjects instead of photographs) are technically non-sports sets, as they are art card sets.
While I don't collect too many sports cards these days, I loved the Upper Deck Baseball and Football Masterpieces sets from a few years ago. All-new paintings on canvas type cards, they were just handsome cards. Upper Deck baseball also had Celebrity and Presidential Predictors which had exquisite painted caricature art. Those cards, although from sport cards sets, are cards that would fit right in just about any non-sports cards collection.

Strictly speaking, I just go by the nature of the set and the background of the person depicted on the card. I have never thought to call a painted card or art card of an athlete in a sports card set as being anything other than a sport card. But if that same athlete appears in a mixed celebrity set, like Americana for instance, than it is a non-sport card to me.

The line gets blurry when you have inserts in sports card sets that involve celebrities or famous historical figures. The Fans of the Game as an example, come from sports card sets, but they are autographs of celebrities picking their favorite baseball and football teams. These cards could easily be regarded as non-sport autographs simply because the signers themselves are not athletes at all.

ProLine Football from 1991 through 1993 had some great non-sports subject in it, I remember cards of Martin Mull and Milton Berle, among others, basically the first "Fans of the Game" type cards. I liked football cards anyway back then, so I'd have bought them anyway, but the celebrity subjects were a real treat.

Right around the same time, Upper Deck made World Cup soccer cards, and while I was not a fan of soccer, they had some great "Honorary Captains" cards in those with athletes from other sports, plus politicians and the like, and those were fun cards to chase, as well.

The original Topps American Pie set from around 2001 was maybe the first modern set with an nearly even mix of athletes and non-sports subjects, and that set was a big hit inspiring a followup a year later.

In the modern day, Panini Golden Age has replicated that formula with a couple of excellent sets, and more and more, sports and entertainment and becoming the same thing, so naturally they are mixing together in cards, too.

"Blurred Lines" are everywhere these days, even at the top of the Pop Music charts!

Yeah, good question! I've struggled for years with some titles. What about these sets:
Eight Men Out
Muscle Cars (and similar sets) but not formula 1
Olympic Cards (of which there are a few sets)
Pro Bodybuilders
All Pro Skateboarders
Baseball's Greatest Grossouts
Hockey Freaks
I'm with Raven on these last two. As I see it they are cartoon sets.

Yeah, any set with the words "grossout" or "freaks" in the title is like a humor set, and Eight Men Out is definitely a movie card set, so non-sport for sure.

Eclipse Comics made some nice boxed sets of cards in the late 1980's and early 1990's and one of those was called "Foul Ball" and it depicted the various misdeeds of infamous players, managers, umpires, etc. from the actual major leagues, but it was a painted art set, so definitely a hybrid.

The Eclipse boxed sets like that were usually 36 cards, and slightly oversized, but they were some great sets, are still affordable these days, and well worth checking out.