Albert Barnes Commentary 1 Samuel 21:7

"Now a certain man of the servants of Saul was there that day, detained before Jehovah; and his name was Doeg the Edomite, the chiefest of the herdsmen that belonged to Saul." — 1 Samuel 21:7 (ASV)

Detained before the Lord

• To fulfill a vow (Acts 21:23–27).
• On account of uncleanness.
• Under the law for lepers (Leviticus 13:4, 11, 21).
• As a proselyte.

It is not impossible that Doeg may have been in custody or in a sanctuary for some crime.