Much of our (scant) knowledge of sanctuary at Westminster Abbey during the reign of Mary I comes from the diary of London citizen Henry Machyn, who recorded notable events in his tumultuous lifetime. Machyn had several entries related to a gentry feud in far-away Yorkshire between the West and Darcy families. First, on 25 May 1556, he reported that “Mr West, esq” (Lewis West) was slain by “my lord Darcy’s son” (George Darcy).
Later he gave details: Darcy and forty armed men set upon West and his six men as he was coming home from Rotherham Fair and shamefully murdered him. This was the third attack on West by the Darcys within two months. It’s hard to say why Machyn found this Yorkshire slaying notable enough to record – maybe it was the talk of the town? This northern drama did have later metropolitan scenes, though, as detailed in some later entries in Machyn’s diary.
Especially interesting for historians of sanctuary is this: on 6 December 1556 the abbot of Westminster went on procession with his monks; before them went “all the sanctuary men with cross keys [a papal symbol] upon their garments.” Clearly sanctuary was connected with renewed Roman Catholicism.
Among those sanctuary men were “three for murder,” including the Lord Darcy’s son George, who “was whipped with a sheet about him for the killing of one Mr West.” The sheet likely meant that he was stripped to the waist, as penitents often were. Darcy had taken sanctuary because he was excluded from a settlement between his father and the Wests to compensate West’s widow (Kesselring, Making Murder Public, 86). I think George’s dad was mad at him. (George was the 3rd son, evidently a bit out of control.)
In Machyn’s last entry regarding this affair, Darcy was arraigned at King’s Bench for West’s murder in early 1558. Machyn cryptically ends his entry by saying “certain men did wage battle with him to fight with combat on a day set.”
What that seems to mean is that Darcy offered to undertake trial by battle – and the men whom Machyn says “did wage battle” were presumably pledging (pledge=gauge=wage) to be his support, rather than that the battle actually did take place. Trial by battle – an alternative to trial – was still technically available in the 16th century but John Baker (Oxford History, 6:351) says it was used only as a tactic “and almost certainly no combat was fought in Tudor times.” That’s true here, too: likely no battle.
I spent some time digging around in the King’s Bench rolls to find the case – it’s long and I didn’t read it thoroughly, but I can’t see anything at all in the roll about trial by battle. Maybe Machyn was mistaken or maybe it just didn’t make it into the official record.
In the end Darcy didn’t need the trial by battle to get out of his situation: ultimately the charges against him and his co-accused were dismissed (as below). I’d guess that this was a result of a further mediation agreement between the Darcys and the Wests.

So all’s well that end’s well, hey George Darcy? Maybe not so much for Lewis West and his widow.
Machyn, Chronicle, fols. 56r, 63v, 87v (https://quod.lib.umich.edu/m/machyn/); TNA, KB 27/1185, plea m. 39.