The Octoball Derby can be found in Lorule. From the Vacant House, go left, down, left, and up into the meadow. Talk to the Derby Boy and pay him 50 Rupees to begin playing.
How to play:
Wait for the Octo to pitch a ball at you and press A to hit it. Break an ordinary pot to earn 1 Rupee. Each golden pot that you break will earn you 5 Rupees. The Crows that fly past occasionally are worth 20 Rupees. A score of 100 Rupees or more will net you a Piece of Heart. You get 30 pitches in total with which to do this.
The timing of your swing affects how far left or right the ball goes. Swinging early will send your shots to the right; a later swing will send the ball further to the left. Holding down on the circle pad will aim your shots up at the treetops and the Crows. Holding up on the circle pad lets you break the pots at the front by bouncing the ball along the ground.
Hitting a crab scores you no points but it will replenish all of the pots that you have already broken. Hitting the Octo will cause him to pitch the next ball much faster.
Since the Crows are worth 20 Rupees, you need to hit as many of them as possible. More Crows will appear if you keep scoring points. Ignore the smaller pots and focus on breaking the gold pots as they appear, one at a time. Any small pots that you break accidentally by missing your target can be considered a bonus. As soon as a Crow appears, watch it fly past and try to predict where it will be by the time you swing. You don’t need as much accuracy to hit the Crows as you do to break the pots – as long as you are in the right area you should be successful. This should rapidly build your score to 100 Rupees or more.
Once a pot in the front row is broken, you can hit pots in the middle by aiming low. The benefit of this is pretty small, but it gives you more opportunities to score points if you miss the target.
If you are really struggling to hit the golden pot that you are aiming for, try shifting your aim to areas with lots of intact pots. You will probably score fewer points but will break more pots – which will help to make Crows appear, and essentially get you a higher score. Keep an eye on how many pitches you have remaining. On the last pitch you should always aim for the most valuable target – either a Crow or a golden pot.