[dagw]

A striker cannot play in central defence, or vice versa

Sure they can. Perhaps not as well, but I bet a premier division striker will easily be able to play defense for a lower division team, and with a bit of experience could probably become really good. Hell I'm sure LeBron James could make a pretty decent soccer player if someone gave him some coaching and the right incentives.

[rglullis]

I really think that we are getting way too sidetracked into the discussion, but I think you are underestimating the amount of fitness (in the evolutionary sense) it is required to be in the top 0,01% compared with the top 1% of any sport. Being a "pretty decent soccer player" will get you nowhere near any league.

Don't even need to get out of football to think of an example where this experiment has failed. Falcão is to this day considered one of the greatest players of indoor football. He tried to get into football by playing for São Paulo FC and stayed in the bench for most of the season, then went back to futsal.

Or if you want to go back to Basketball: Michael Jordan and his baseball career.