A ram was sacrificed by the rex sacrorum, a priest of Jupiter. The festival may have honored multiple gods.
In his Fasti, Book I. lines 317-458, Ovid lists six possible etymologies for the Agonalia, according to Frazel ("Ovid 'Fasti' 1.325-26, and 'Lamb Festivals,'" by Thomas D. Frazel; Classical Philology , Vol. 97, No. 1 (Jan., 2002), pp. 88-92)
1. The day may take its name from the girded priest At whose blow the god's sacrifice is felled:
Always, before he stains the naked blade with hot blood,
He asks if he should (agatne), and won't unless commanded.2. Some believe that the day is called Agonal because
The sheep do not come to the altar but are driven (agantur).3. Others think the ancients called this festival Agnalia,
'Of the lambs', dropping a letter from its usual place.4. Or because the victim fears the knife mirrored in the water,
The day might be so called from the creature's agony?5. It may also be that the day has a Greek name
From the games (agones) that were held in former times.6. And in ancient speech agonia meant a sheep,
And this last reason in my judgement is the truth.Translation provided by A.S. Kline: Ovid Fasti Book I

