If there’s not enough room to Swing a Cat then the space is very small and tight. It has been suggested that the phrase originated from when sailors, in the 17th century, needed space in which they could swing the cat o' nine tails. However there is evidence from about two centuries earlier and involves actual cats. In the 15th century there was a “sport” which involved the swinging of cats, by the tail, into the air. In this way, they would become moving targets for archers at fetes and country festivals. So, if a festival was very crowded, it would be described as having no room to “swing the cat”.