The wording of the Hebrew text indicates simultaneous action. So the translation should also indicate that the Philistines were moving into position to attack the people of Israel at the same time that Samuel was in the process of offering the sacrificial lamb.
Thundered with a mighty voice: probably a violent thunderstorm (see also 2.10; 2 Sam 22.14). But this may be difficult to translate naturally in certain languages. Some possible models are “the LORD roared like thunder” and “the LORD shouted from heaven and his voice sounded like thunder.”
Threw them into confusion: the same meaning may be conveyed by making the Philistines the subject of the sentence instead of keeping Yahweh as the subject. God caused the Philistines to be confused, so it is possible to say “they were confused” or “they were so frightened they became confused” (New Century Version). In Psa 55.2, where the Psalmist says “I am distraught,” the same Hebrew verb is used.
They were routed before Israel: see the same verb in 2 Sam 22.15. Verse 11 states that the Israelites pursued the fleeing Philistine soldiers, but here in verse 10 the Israelites have no part in the defeat of the Philistines. It is God alone who defeats the Philistine army in the presence of (before) the soldiers of Israel. The fighting was done by God, and all that remained for Israel was to pursue the fleeing Philistines (verse 11). It seems wise, therefore, not to follow those translations such as New American Bible, New Jerusalem Bible, New Jewish Publication Society’s Tanakh, New Living Translation, and Bible en français courant, which state at the end of this verse that Israel defeated the Philistines or “they were routed by Israel.” In languages that must use an active form of the verb, it will be necessary to say that “God routed the Philistines before Israel” or “God caused the Philistines to flee.”
Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on the First and Second Books of Samuel, Volume 1. (UBS Helps for Translators). New York: UBS, 2001. For this and other handbooks for translators see here .