rookie mistakenoun [ C ]
uk/ˈrʊk.i mɪˌsteɪk//ˌˈrʊk.i mɪˌsteɪk/mainly US also rookie error, /ˈrʊk.i ˌer.ər//ˈrʊk.i ˌer.ɚ/, UK also schoolboy error, /ˈskuːl.bɔɪ ˌer.ər//ˈskuːl.bɔɪ ˌer.ɚ/a basic mistake, like one that a person with no experience of an activity would make:
Although he's an experienced movie director, he made the rookie mistake of trying to cram too much material into a mere 100 minutes.