3rd Gen Splash causing damage

I remember back when i first played emerald i encountered a magikarp in sootopolish city which used spash on my pokemon and it actually did a small amount of damage.
It did 2 hops then went a little back then came to the front with a bam like megapunch.
Has this happened to anyone else?

That was probably Flail. If you're still confused, feel free to ask in the Q&A thread, but you'll likely get the same answer.

Locked.