The phrase "inept performance" refers to someone's poor or unskilled display of their abilities or task. It means they did not do a good job and struggled to perform well. Full definition
Giroud is our best striker inspite of his last inept performance against Monaco. (justarsenal.com)
Yesterday was as inept a performance as we have seen all season; right down there with the capitulations against the other fellow relegation candidates such as Newcastle and Brighton. (westhamway.net)
Sean McMeekin's July 1914: Countdown to War (Basic Books) lays primary blame on Austria - Hungary; Christopher Clarke's The Sleepwalkers: How Europe Went to War in 1914 (Harper) and Max Hastings» Catastrophe 1914: Europe Goes to War (Knopf) spread the responsibility around, with both Clarke and Hastings assigning Wilhelmine Germany the decisive role amidst a desperately inept performance by the Great Powers. (firstthings.com)