How many chicks do you have? Is it only one doing this? Is it constant or just sometimes? What are you feeding? What's the temp in your brooder? Where are you located?
If this is happening every now and then, it's probably the cecal poop (happens ever 6 - 7 poops) and normal. If it's every poop, it's possible your booder is too warm. Just a few possibilities, others will peep in their thoughts.