If both parties are given an infringement notice for fighting in a public place. Only one has paid their fine. The one that hasn't paid now wants to take it to court, what happens to the one that has paid his fine?
Using New South Wales as an example
(and without knowing important specifics
such as what state you are in,
or in respect of what law you were issued the Notice),
consider the following.
Worry about yourself, not the other guy.
You need to be clear if it was an Infringement Notice
(a "ticket", so to speak), or if it was a "CAN" (a "Court Attendance Notice",
which means, yes, you do have to go to court).
I will assume for the present that what you have is an "Infringement Notice".
Generally speaking, Infringement Notices are issued to individuals, each,
in respect of THEIR particular actions, even if they come from the same set of facts.
As a general thing, (exceptions excepted and many variables not allowed for)
each recipient of an Infringement has the option to pay the fine,
or to "court elect" (that is, have the matter dealt with by a court).
It makes no difference to YOU what any other recipient of a similar notice chooses to do.
If you have have paid your fine, but the other guy has not, then that has no effect on you.
It's over, get on with your life.
If you are the guy who is court-electing YOUR infringement, then you need to be aware of,
among other things, the timeframes involved. For example, there may be only a certain number of days in which you can lodge a court-election, before the matter becomes an unpaid fine.
As a general rule, if you pay the fine, then that is the end of the matter.
It's over, go get on with your life.
On the other hand, if you go to court and you are found guilty,
you may be convicted of the offence (sometimes, in NSW at least,
you can be given a bond with no conviction recorded).
A conviction (even a minor one) can have knock-on effects
for your work prospects and for your personal life
which you may not have even thought of.
Putting aside emotion for a minute, (and by that I mean general resentment,
anger, and any questions about unreasonableness of the person who issued you the Notice),
ask yourself if you are genuinely not guilty, and if not, what is the simplest way to
Just Deal With It.