In may 1400 William Hay of Yester accompanied George the 'Red' Douglas Earl of Angus of Tantallon castle to a meeting at Bothwell castle with Archibald the 'Grim' 3rd Earl of Douglas , to defuse an ongoing feud between the 'Red' Douglas and James Douglas of Dalkeith (Archibald's ally) over possession of the lands of Liddesdale. The 'Red' Douglas and his allies had burnt the lands around Dalkeith castle and other estates throughout Scotland "To recover from James Douglas all mails and rents of Liddesdale which he wrongfully occupies." Eventually an agreement was made where the 'Red' Douglas faction would end their attacks in exchange for some of the Liddesdale lands.
In 1402 William Hay of Yester marched on Newcastle with the Scots army under the command of Archibald 4th Earl of Douglas . After retiring from Northumberland the Scots carrying much booty were intercepted and routed by 'Hotspur' Percy and his expert Welsh archers at the Battle of Homildon Hill , near Wooler. William Hay along with the Earl of Douglas was among the many nobles unhorsed and captured during the battle. By 1403 Hay of Yester was back in Scotland signing land charters for the still captive Earl of Douglas. At this time a dispute arose between the Percies and King Henry IV of England over who could claim the ransom money for the many Scots nobles taken at Homildon. This led to open rebellion where 'Hotspur' Percy led Welsh and English rebels against King Henry at the Battle of Shrewsbury . During the battle 'Hotspur' was killed and the rebels defeated.
In 1407 the Earl of Douglas appointed 'his very dear squire' William Hay as Sheriff of Peebles. Later he also gave Hay lands in Galloway. By 1418 Douglas orderd his men to 'impose distress' on the people of Galloway for refusing to pay their rent to their new Master William Hay. Showing that he like his father Archibald the 'Grim' ruled by fear and force of arms.
In 1409 Margaret, daughter of William Hay, married William the 'Red' Douglas, 2nd Earl of Angus in an attempt to bring the 'Red' Douglases back into the fold of the 'Black' Douglas camp. With the death of William Hay in 1420, his son Thomas took over as Lord of Yester
