Who is "ha'Doleg Al ha'Miftan"?
Rashi citing Targum Yonasan: They follow the etiquette of the Pelishtim. They did not step on the threshold of Dagon (their god) - "Al Ken Lo Yidrechu Chohanei Dagon [Al ha'Miftan]" (Shmuel I, 5:5).
Radak citing his father: These are servants of the officers, or youths of the king. When they saw in an Oni's house an item that they coveted, for it was nice, they ran inside amidst frenzy to take it and bring it to their master - "ha'Memal'im Beis Adoneihem Chamas u'Mirmah."
Radak citing Ibn Ezra: This refers to the threshold of their masters' houses. Amidst Simchah that they come to fill their masters' houses with theft and [items obtained via] deceit [they appear to jump over the threshold].
Radak citing Yalkut Shimoni 566: Yisrael were more stringent about idolatry than the nations. Yisrael jumped, whereas the nations "Al Ken Lo Yidrechu Chohanei Dagon Al ha'Miftan 1 ."
Malbim: The servants of the officers. Just like Kohanei Pelishtim [did not step, rather,] jumped over the threshold when they went to their place of awe, so the servants did when going to their masters' houses to fill them with theft and deceit. They are the enforcers to oppress and extort!
I.e. the nations stepped next to it, just not on the threshold. Yisrael jumped, to distance from stepping on it. (PF) Yerushalmi Avodah Zarah 3:2 - the nations honored only one threshold of idolatry; Yisrael honored many.
