Mr Football is a game many years in the making, with many antecedents influencing the final product.
The primary source was Star Trek Timelines, as many screens mirror its design as well as player levelling and the challenge system. STT itself is built on the hero collection game template started by Heroes Charge, Summoners War and similar Chinese card-based RPGs.
A lot of the original design of Mr Football came from Blood Bowl, another attempt to turn the chaos of team contact sport into a board game using six-sided dice… as well as creating an alternate history. Its seasonal campaign design teaches a lot about how to develop a sustainable player development system, and the fan site FUMBBL was also an influence with its league design. The concept of seasons where player cards and soft currencies are wiped is also shared by FIFA Mobile, and though it was not an inspiration it did show that you can do that while still keeping coaches interested between seasons.
Finally, the inspiration originally came from Hounded 2, a greyhound management simulation developed for the Commodore 64 by South Australian accountant Kelvin King in 1985. What a legend! The game was written in BASIC, and Kelvin left messages in the code for hackers to find detailing how he created it.