As long as F1 throws to the base at 1B only, it is not a balk. If he throws to F3, then F3 better be at the base or have a legitimate chance to retire a runner. But, he doesn't have to actually retire a runner.
Ok, thanks! I booted one...F3 was playing about 10 feet off the base about even with the runner and the pitcher threw to the bag. In this league it was a warning for the balk, but it still irks me that I missed it.