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Was this like the previous time that Sha'ul tried to strike David with a spear (18:10, 11)?
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Malbim: No. (a) Then, he took the spear while David was playing, so David did not notice. Here, he held the spear from the beginning, so David knew to beware. (b) There, it says "va'Yatel" - he cast it to and fro, so it would look like he struck David b'Shogeg. Here he overtly intended to strike him. 1
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Above (18:11), Malbim explained "v'David uva'Kir" - I will make it look like I did not intend for David, only for the wall. It says the same expression here! (PF)