"Pick up volleyballs" is an objective in the sidequest Too Close For Missiles in Borderlands 2
Walkthrough[edit]
Volleyball 1
Head over to the West and go against the railing on the right. You will see plenty of bandits en route. Head past the first buzzard launch pad on the right then jump down over the railing. Deal with the bandits and head for the shack just up the short stairs. There you will find the first Volleyball.
Volleyball 2
Head on up the stairs just to the West of where you found the first ball. Go to the South and climb onto the angled strut to your right ahead of you. Walk up it until you are over the first bungalow. Drop down onto it and you will find the second Volleyball.
Volleyball 3
Drop off the bungalow to the East. Look by the massive tank to find the first Gas Can. Just go to the East and drop the slope. Look to the North from where the Volleyball Net is. You can see the volleyball on top of a tower. Head to the left of the tower and onto the platform just after the bungalow. Jump from onto the bungalow, to the next platform and onto the tower.
Volleyball 4
Head to the Northeast. Drop down onto the ledge and go over to the Eastern edge of it. There you will find the final volleyball sitting underneath a shelter.
