The phrase "knocking props out" is spelled with the silent letter "k" at the beginning of "knocking" and the cluster of consonants "kn" at the beginning of "knocking" and "props". The correct pronunciation is [ˈnɑkɪŋ prɑps aʊt], with the "k" sound not pronounced. "Props" is often spelled with a final "s" but should be pronounced [prɑps] with a voiceless "p" sound at the beginning. The phrase means to undermine or weaken someone's confidence or support.