Dips in, a-rse

Gillespie, the fifth highest wicket-taker for Australia with 251 Test wickets, also argued that his ineffective performances were not a result of poor form. "I don't think I lost form that dramatically. Yes, I was not at my best. Yes, I got only three wickets for a fair few runs, but I wasn't bowling absolute rubbish.

"In the first Test I didn't get a big run. In the second I was OK but a bit below par. Then I had a bad game at Old Trafford and I was out. I didn't think my world had caved in. People said it was the end of me. I had a laugh about that. It was as if I'd lost all my skills or was the worst bowler in the world. People can have dips in form. For me, it was a mixture of bad bowling, good shots and a-rse. You've got to react and adapt, and I didn't do that well enough."

Please explain to me the highlighted parts. The dictionary shows "a-rse" means flesh back part of an animal (used to sit), but it doesn't fit in this context.