You may have a case IF it would be considered "negligent"--or unreasonably careless--to have a sprinkler hole of that size in that location. If it was, you could possibly recover your out-of-pocket medical costs (not picked up by insurance); lost wages (if you missed work); and potentially pain and suffering if you suffered any relatively long lasting impairment of life functions or enjoyment. If you were not injured to any extent, there's no point in suing--you'd spend more on the lawsuit than you'd recover.