Well it really depends. But yeah soccer is
- as tough as a fight sport. The kicking, pushing, elbows and etc are insane and usually they are between two players running at full speed at each other. The injury rate is also insane. I have had less injuries in boxing than in soccer
- enduarance and especially performing when tired - you run for 90 mins with a 15 min break in between and you end up with about 8-15 km ran at the end and some of these kms are full speed 20-40 meter sprints
- technique with the ball - now that is something else. Most people can dribble with a basketball or throw with some accuracy with hands, but making an inch perfect pass with the required speed of a delivery, so your team mate can make a good first touch requires a lot of drilling, fantasy, technique and etc. The mind connection between dribbling, passing, shooting - you either have or you do not. This is where soccer is special. Technique with the ball.
- tactics - and after all that you get to the 50% of the game - the tactics. The game is so complex that it requires top coaches and tactics gurus to come up with a strategy for a whining team. There are like 15-20 zonal positions and all of them can be played in a different way. And Ronaldo perhaps was a very good right winger when young (due to speed), then good left inside forward in peak (due to athleticism and shooting technique) and now a central forward (due to developed sense of scoring, shooting technique - when older), but the guy would suck in most other positions and be average or below average in them. So Ronaldo the forward is world class, but Ronaldo the defender would not make a living as a professional footballer for example. Additonally to tactics - there is no other sport that is that much developed into this field as tactics in football.
In the end the Bolt comparison is just ridiculous.Boxing to MMA is not like running to soccer. Soccer is way more complex, has traditions and etc. Lets not make it that MMA is a rocket science. You go in as a world class boxer, chance you are successful with some training of course under MMA rules are pretty high. Otherwise top wrestlers would suck in MMA too. Having in mind wrestling does not have a professional scene and is quite under developed in comparison to boxing, I have no clue why people can not graps it that a professional world class boxer would do just fine and has an easy transition if not an easier one that a wrestler into the sport of MMA.