I was going to suggest the Canon 70-200 f4L IS until I realised you were looking for something LONGER.
I have had this lens for a few years now and the build and image quality is stunning.
I have used the Canon 100-400 and it may well suit your needs for the football.
The only thing I wasn't sure of with this lens was the push-pull zoom mechanism, but I soon got used to it and thinking back it was the same mechanism used on all my film zooms from the 80s.
If I add another lens to my kit it will almost certainly be the Canon 100-400 for sport and wildlife.
As far as flora goes, have you thought about a macro and getting in close?