Re: is the reason for/subject/object
If you want 1 and 2 to mean the same thing, then use 2. It's much more natural.
Originally Posted by navi tasan
3 is OK but again, it would be better to personalise it with "Infidelity is the main reason people file for divorce".
I don't like 4. It almost sounds as if the referee is the one who commits the foul, or at least it doesn't make it clear who committed the foul. "Committing a foul is the main reason players get sent off" is much clearer.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.