Sports cards that are worth money share three properties regardless of sport: small supply, good condition and present demand. What changes between sports is which cards happen to have all three, and that is a matter of each sport's production history rather than of any difference in how value works.
The supply signals are identical
A printed serial number, a documented short print, a manufacturer autograph, a genuine game-used swatch, or a date from before production rose. Those five features mean the same thing on a hockey card as on a baseball card, and in every sport a base card from a mass-produced set fails the test however famous the player.
Condition is judged the same way
Corners, edges, surface and centring, assessed against a white background under decent light. The only sport-specific note is that modern foil-fronted cards, which are most common in basketball and football, show handling more readily than older matte cardboard does.
Demand is where the sports actually differ
Baseball has the deepest market for older cards. Football concentrates on quarterbacks and rookie years. Basketball is the most volatile, moving with form inside weeks. Hockey trades thinnest, so its cards are harder to price from few sales. Those differences change how you read the sales, not what the sales mean.
And the arithmetic is universal
Five completed sales of the exact card in your condition, the extremes dropped, the middle three averaged, the spread read. That works in any sport because it is a way of summarising a small sample rather than anything about cards, and it is what the checker on this site does.
Questions people ask about sports cards that are worth money
Which sport should I check first?
Whichever your best cards are in. The sorting features are identical, so there is no advantage to starting in one sport over another.
Can a hockey card be worth as much as a baseball card?
Individual cards can be worth a great deal in any sport. The market's depth differs, which affects how quickly a card sells rather than whether it has value.
Are multi-sport cards a thing?
Some sets and some athletes cross sports, and they are priced by whichever collector base is bidding. The sales record tells you which.
Does the same grading logic apply in all four?
Yes, with the caveat that the size of the graded premium differs by market, which is visible in completed sales at each grade.