An appeal is defined in the Official Baseball Rules as "the act of a fielder in claiming violation of the rules by the offensive team."
The appeal here is that the offense failed to touch first base, as in OBR 5.06(b)(1), and the rule stating the runner shall be called out on appeal is 5.09(c)(2) ("fails to touch each base in order before they, or a missed base, are tagged").
This Teachable illustrates how to rule on this appeal and how to recognize when the defense is appealing.
Alternate Link: Tosi rules runner out on appeal for missing a base in San Francisco (CCS)
