Scary Pool Experience

One time, i went swimming with my big sister, she was 20 and i was 13-14 years around that time. I remember an old man jumping into the pool when we were in and my thought was to just ignore him and all of a sudden i saw him coming closer. I was thinking he was coming to meet my sister since she was older than me but instead he went under and grabbed my legs which scared me. I was lucky my sister was with me and she turned around and started shouting and then he left