Knock here in the sense of "knock into" or "knock out".
Mnemonic
[k-] Kermit the Frog is in [1] front of the [-e] electricity plant. Not looking where he is going, he accidentally 磕 knocks into a large stack of 皿 dishes that are on the concrete with his 厶 elbow. The 磕 knocked into 皿 dishes fall over into the 土 soil. The electricity plant guards run out and start throwing 石 stones at Kermit for 磕 knocking into the 皿 dishes.