pace

The pace of the game goes fast.

Pace is simply how fast something is being done. See additional examples below:

1. Her pace wasn’t as fast as last week, so her time in the running event was much slower.
2. Pick up the pace! We’re almost out of time.

end up

When I play rugby, I end up hurt for a week but it's a good kind of pain.

End up refers to the results or the consequences of doing something. Here are two more examples:

1. He drives like a maniac. He is going to end up in the hospital.
2. We ended up leaving the party early because we were so tired.

back and forth

I think it's so cool to watch the ball go back and forth.

Back and forth is the same as backward and forward and it also implies that it is happening repeatedly. See the examples below:

1. My girlfriend lives in a different city so I’m always driving back and forth between her city and mine.
2. We have been sending e-mails back and forth to each other for about a year now.

organized sports

I have to say I don't really enjoy team sports or organized sports.

Organized sports are when you play on an official team with uniforms, coaches, referees, and a schedule of games. IHere are two more examples:

1. I played sports a lot when I was young, but I never played organized sports.
2. I’m not sure why organized sports get so much attention. I’d rather see really talented artists playing music.

not keen on

I'm not so keen on competitive sports anymore though I used to play soccer quite a lot.

Not so keen on something means that you don’t really like it. See the following examples:

1. I’ve never been so keen on chocolate.
2. After about 3rd or 4th grade, most kids aren’t so keen on school.