The question regarding 1 sam 18:10 must also be read in the greater contect of 1 Samuel in general. This isn't the first time that the spirit of God had rushed Saul. Cf 1 Sam 10:10: (ESV)
10 When they came to Gibeah, behold, a group of prophets met him, and the Spirit of God rushed upon him, and he prophesied among them.
Second, It also identified Saul as a false prophet in the later incident. Cf 1 kings 22:21-23:
Then a spirit came forward and stood before the LORD, saying, ‘I will entice him.’ 22 And the LORD said to him, ‘By what means?’ And he said, ‘I will go out, and will be a lying spirit in the mouth of all his prophets.’ And he said, ‘You are to entice him, and you shall succeed; go out and do so.’ 23 Now therefore behold, the LORD has put a lying spirit in the mouth of all these your prophets; the LORD has declared disaster for you.”
Thirdly Saul is not to be feared cf Deut 18:22:
22 when a prophet speaks in the name of the LORD, if the word does not come to pass or come true, that is a word that the LORD has not spoken; the prophet has spoken it presumptuously. You need not be afraid of him.
In fact Saul became or even dreaded David: 1 sam 18:12
Saul was afraid of David because the LORD was with him but had departed from Saul.
Why you ask? Because God said through the Prohpet Samuel that Saul will not establish a dynasty. 1 sam 15:22:
22 And Samuel said,
“Has the LORD as great delight in burnt offerings and sacrifices,
as in obeying the voice of the LORD?
Behold, to obey is better than sacrifice,
and to listen than the fat of rams.
23 For rebellion is as the sin of divination,
and presumption is as iniquity and idolatry.
Because you have rejected the word of the LORD,
he has also rejected you from being king.”
cf 1 sam 16:13:
Then Samuel took the horn of oil and anointed him in the midst of his brothers. And the Spirit of the LORD rushed upon David from that day forward. And Samuel rose up and went to Ramah.
The promise of Christ resides in David, not Saul. Recall Saul's pride was the cause of his disobedience and now the Lord has given him over to his pride. It is judgement.