I think my definition of G.O.A.T is a bit different than most....I consider on field accomplishments, but also the impact they had on the game as well as accomplishments after leaving, that being said...
Football-Walter Payton (lol the top college offensive player doesnt get the Tom Brady award, neither does the NFL man of the Year
Boxing-Muhammed Ali (monster in the ring at 18 as well as 33, stood up for his beliefs despite the negative impact, not to mention all of his humanitarian efforts his whole life
Baseball-Nolan Ryan (heck the Robin Ventura fight should be enough! 46 yr old pitcher giving more than he got from a 26 yr old!)
Basketball-Michael Jordon (the game of basketball was literally reinvented by the way MJ played the game)
lol Im reminded of when Larry Bird was asked about who would win...the original Dream Team or the new Dream Team, everyone was shocked when he said the new Dream Team, then followed it up by saying he hadnt picked up a basketball in 15 years so they the new Dream Team would have the edge