It's simple, having top football players play football and top cricket players play cricket is all well and good, but for a real challenge of these top athletes we should mix it up a bit. With team sports most sides will have a squad large enough to deal with the variations in number, so we could have
teams play sports other than the ones they are trained for. There are various scenarios which spring to mind straight away:
April Fools Day, a series of exhibition matches raising money for charity. See the Manchester Derby take place as an Ice Hockey game, while rugby teams kick the ball around at Old Trafford. We could even mix and match some more, as The Harlequins from the Rugby Union take on Everton FC in a cricket match. Could also work for Sports Relief.
A game show, where various clubs try to earn points to win an alternative league in other sports. Sussex may be good at cricket, but are they real all-rounders?
A gamble. The Premier League is considering adding a 37th game onto the season where teams have to hope for the lucky match-up, let's take it further whereby they get given a non-football team that will represent them, they then have 2 weeks to try and train them in the beautiful game before they go out on the big stage and compete in the actual league (Faking it-esque).
We all used to swap classrooms on April Fools when we were younger, let's continue the tradition to the big leagues, literally.