Hi all

Recently i finished building my first fixed gear bike and have been riding it a fair bit over the past 2 days. I went out for a ride into town tonight as i was peddling quite hard BOOM there was a big jerk/slip in the chain. Theres nothing wrong with the chain and it hadn't slipped off. I went a bit more and the same thing happened. I thought since some of you are experts on the matter you could maybe give me an insight as to what might wrong. Im guessing something to do with the rear hub/cog. I dont want to start striping everything off if i have no idea what im looking for. Any help would be much appreciated. Thanks.