A.T. Robertson Commentary Mark 9:20

"And they brought him unto him: and when he saw him, straightway the spirit tare him grievously; and he fell on the ground, and wallowed foaming." — Mark 9:20 (ASV)

Tare him grievously (συνεσπαραξεν αυτον). Luke 9:42 has both ερρηξεν (dashed down, like Mr 9:18, ρησσε) and συνεσπαραξεν (convulsed). This compound with συν- (together with), strengthens the force of the verb as in συνπνιγω and συντηρεω (6:20). The only other instance of this compound verb known is in Maximus Tyrius (second century B.C.).

Wallowed (εκυλιετο). Imperfect passive, was rolled. A pitiful sight. Late form of the old κυλινδω.