Where does “färsking” come from?

färsking (Swedish) comes from Swedish -ing, from Old Swedish -ing, from Old Norse -ing, from Proto-Germanic -ingō — -ing.

färsking (Swedish): a rookie, a newbie

Definitions

Step	Language	Word	Meaning
1	Swedish	-ing	Used to form verbal nouns from verbs; -ing. See...
2	Old Swedish	-ing	Forms gerund nouns from verbs
3	Old Norse	-ing	Forms gerund nouns from verbs
4	Proto-Germanic	-ingō	-ing