described in "Cormac's Saga", ch. 10, may have been Saxo's authority.
The combatants change places accidentally in the struggle in one story.

The combat might last, like Cuchullin's with Ferdia, several days; a
nine days' fight occurs; but usually a few blows settled the matter.
Endurance was important, and we are told of a hero keeping himself in
constant training by walking in a mail coat.

The conqueror ought not to slay his man if he were a stripling, or
maimed, and had better take his were-gild for his life, the holmslausn
or ransom of "Cormac's Saga" (three marks in Iceland); but this was
a mere concession to natural pity, and he might without loss of honor
finish his man, and cut off his head, though it was proper, if the slain
adversary has been a man of honor, to bury him afterward.

The stakes are sometimes a kingdom or a kingdom's tribute, often a lady,
or the combatants fought for "love" or the point of honor. Giants
and noted champions challenge kings for their daughters (as in the
fictitious parts of the Icelandic family sagas) in true archaic
fashion, and in true archaic fashion the prince rescues the lady from a
disgusting and evil fate by his prowess.

The champion's fee or reward when he was fighting for his principal and
came off successful was heavy--many lands and sixty slaves. Bracelets
are given him; a wound is compensated for at ten gold pieces; a fee for
killing a king is 120 of the same.

Of the incidents of the combat, beside fair sleight of fence, there is
the continual occurrence of the sword-blunting spell, often cast by the
eye of the sinister champion, and foiled by the good hero, sometimes
by covering his blade with thin skin, sometimes by changing the blade,
sometimes by using a mace or club.

The strength of this tradition sufficiently explains the necessity of
the great oath against magic taken by both parties in a wager of battle
in Christian England.

The chief combats mentioned by Saxo are:--

Sciold v. Attila. Sciold v. Scate, for the hand of Alfhild. Gram v.
Swarin and eight more, for the crown of the Swedes. Hadding v. Toste, by
challenge. Frode v. Hunding, on challenge. Frode v. Hacon, on challenge.
Helge v. Hunding, by challenge at Stad. Agnar v. Bearce, by challenge.
Wizard v. Danish champions, for truage of the Slavs. Wizard v. Ubbe,
for truage of the Slavs. Coll v. Horwendill, on challenge. Athisl v.
Frowine, meeting in battle. Athisl v. Ket and Wig, on challenge.