1) Usually said to mean carrier or pedlar (OED).
However, the by-name occurs two centuries before examples quoted in the dictionary, recorded in 1306 in Derbyshire where the connection may have been with lead-mining: 1306 Thomas le Jager , Longstone. The first Yorkshire examples refer to a family which became established in Stainland, but the ‘le’ which would point to an occupational name has not been noted: 1349 John Jagger
1400 John Jager
1450 John Jagger and the meaning in this case remains uncertain. As a vocabulary item the word is rare in Yorkshire but it occurs quite late, in a lead-mining region where Derbyshire men are known to have worked: 1705-8 Ralph Orton ... being then a jagger brought lead from the said mines to Richmond , Grinton. Although Orton is more characteristic of the Midlands than north Yorkshire, this family had been established in Swaledale from the 1500s at least. Both ‘jag’ and ‘jagger’ have a strong association with the midlands.