1)
When did Ru'ach Elokim come on Sha'ul?
1.
Radak: It was when he was on the road, before coming to Nayos.
2)
Why did Ru'ach Elokim come on Sha'ul?
1.
Malbim: It says "Gam Hu" - he was already prepared for Nevu'ah. He already had Nevu'ah once, therefore the Ru'ach came on him from afar, unlike his messengers, who had Nevu'ah only in front of Shmuel.
