An assist is not a concept the laws of football recognize. It exists only because competitions and data companies decided to count something, and each of them defined it separately.
There is no governing definition
Goals are defined in the laws. Assists are not, which means no body has authority to say what one is, and none has ever claimed it.
Competitions therefore publish house rules. A league's official assist may require the final pass, or may allow one intervening touch, or may exclude passes that were deflected.
Data providers add their own variants because clients want them. The same pass can be an assist in one feed and not in another, with both feeds correct by their own rules.
The disputed cases are predictable
A pass that a defender deflects before reaching the scorer is the classic disagreement. Some definitions strip the assist entirely, others keep it if the deflection did not change much.
A won penalty is another. Some records credit the player fouled with an assist on the resulting conversion, while others hold that no pass occurred so nothing should be credited.
Rebounds sit in the same territory. A saved shot that falls to a teammate may credit the original shooter, or may credit nobody, depending on the rulebook in use.
Why baseball's version is cleaner
Baseball's assist is defined in an official rulebook maintained by the sport itself, and every scorer works to that document. Disagreements are about application, not about definition.
Basketball sits between the two. The assist is defined by the league and recorded by trained statisticians, but the requirement that the pass directly led to the basket still involves judgment.
Football never established either mechanism because the statistic was invented externally. It arrived through media and broadcasting rather than through the sport's own record-keeping.
What this does to comparisons
Cross-competition assist totals are effectively unusable without knowing whose definition produced them. A player moving between leagues can see the number shift for reasons unrelated to play.
Career totals compiled across competitions inherit every definitional boundary they cross. Nobody publishes the seams, so the aggregate looks smoother than the underlying data is.
Historical comparison is worse again, because definitions have been revised. A total from an earlier decade counted something slightly different from what the same league counts now.
Why analysts moved past it
The response has been to build measures that do not depend on a contested label, such as counting passes that create shots regardless of whether the shot went in.
Those measures are more stable because their definition is mechanical. A pass either preceded a shot or it did not, and no judgment about contribution is required.
The assist survives anyway because it is legible to a general audience. It persists as a broadcast statistic rather than as an analytical one, which is roughly where it belongs.

