Skills are very broad for ease of play, but sometimes it's dramatically appropriate to emphasize when a character is out of his element.

When a hero finds himself using a skill in a dramatically different way than he's used to, he suffers a -2 penalty to his rolls. How long this lasts depends on the skill, but should typically be at least a few days of casual use, or a few hours of more intensive use.

What a character is familiar with should be based on his background and any character history the player has written up, with the Game Master having the final say.

If you want more in-depth rules, see the Skill Specialization Setting Rules on page 110.

Savage Worlds Deluxe Edition p. 23