Big lump on head

[GrimDaddy]

One of my black stars has acquired this massive lump on her head. About 6 weeks old. Anyone have any ideas what's going on? Is it serious?

 

[Emelyn]

One of my black stars has acquired this massive lump on her head. About 6 weeks old. Anyone have any ideas what's going on? Is it serious? View attachment 2760667View attachment 2760669View attachment 2760671

Attached below is a forum with the same problem here's a link to it (it's from 2015 but still has a lot of good info!)

https://www.backyardchickens.com/threads/bump-knot-lump-on-chicks-head.981735/