‘ And the king said to Doeg, “Turn you, and fall on the priests.” And Doeg the Edomite turned, and he fell on the priests, and he slew on that day four score and five persons who wore a linen ephod.'
Then Saul turned towards the only man who appeared to be in sympathy with what he wanted. Perhaps as a newly converted Edomite he would not have the same built in qualms of an Israelite. And he was right, For when he called on him to turn and fall on the priests, Doeg gladly obeyed, probably along with some of his shepherds. Shepherds were notorious for their godlessness (their very occupation prevented regular worship at the Sanctuary). And that day Saul's chief shepherd turned on the chief shepherds of YHWH and cut them to pieces, all eighty five of them.
“Four score and five persons who wore the linen ephod”. The linen ephod was the sign that they were qualified to act as High Priests in an emergency. They were the true priesthood. So the ‘holiest' men of Israel, whose lives were taken up in the service of YHWH, were being murdered. The partial effects of this is seen later in 1 Chronicles 24:4 when the sons of Ithamar could not raise more than eight ‘chief men' to be over the orders of the priests in the Sanctuary, compared with Eleazar's sixteen.
(As with all numbers in ancient times, however, the number may not be intended to be seen as mathematically accurate. Most did not think mathematically in those days, and no one would have made a head count. Larger numbers were rather intended to convey an impression. Thus this may represent four full priestly groups and a part group of novitiates or reserves awaiting appointment to a group, all of course descended from Ithamar, Aaron's son).