Yep, a discus.

My son has taken an interest in middle-school track and field and has decided to throw the discus. Throwing the discuss well at this level depends more on having good form than being strong, so practice helps. But practicing with a competition discus has potentially lethal side effects for unwary passerby's at the park.

So I made my son this light weight practice discus that will merely stun, not kill, said passerby's. My son can throw it around and practice his technique without having to go a real netted-in discus throwing ring.

It is the size and shape of a 1kg Junior discus, but substantially lighter. Paradoxically it seems harder to throw flat.

Print four copies of the STL and glue them together. Make the seam on the top and bottom perpendicular. Then go and act out your Olympic fantasies.