Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
This happened to me with zapdos when I was a kid which lead to me thinking pokeballs would instantly fail on legendaries if they didn't work the first time.
:(
i recently tried to catch tapu fini in usum and it also killed herself with struggle. but fini also has aqua ring in that battle and thats just evil.