Im playing Heart Gold, and I am trying to get Raikou and Entei. The first time i saw them i tried to quick ball them. I got it down to three nudges both times, but they got out and fled. Later I got them to low health, but them to sleep, and they fled, so i ran into Entei again and tried to use a quick ball with low health and sleep. It broke out without even a nudge. This happened multiple times. Does this mean that it counts as an ongoing battle? Is that why my quick balls won't work? This happened with Thundurus too in white.
The only thing for you to do here is to either keep throwing quick balls, or use a move like mean look on it. You could also use a pokemon with the ability arena trap or shadow tag as well. Don't worry, you will catch it, just keep trying!
Catch a Bronzong and learn it block