Out of the base path calls near first base are one of the only instances in which painted lines on the baseball field are helpful for adjudication. This is because the distance from the foul line to the lane line along the first baseline is exactly three feet, by rule.
To review, out of the base path is as follows: "Any runner is out when they run more than three feet away from their base path to avoid being tagged unless their action is to avoid interference with a fielder fielding a batted ball. A runner’s base path is established when the tag attempt occurs and is a straight line from the runner to the base they are attempting to reach safely" (Official Baseball Rule 5.09(b)(1)).
While the runner's lane interference rule, as pertains to the physical markings on the ground, states: "The chalk lines marking the threefoot lane are a part of that lane and a batter-runner is required to have both feet within the three-foot lane" (OBR 5.09(a)(11)).
So although the runner's lane rule itself bears no relevance to this tag play at first base, because Solano was positioned on the fair territory side of the runner's lane at the beginning of F3 Soderstrom's tag attempt, and because Solano then ran onto the foul territory side of the runner's lane, we know that Solano must have run more than three feet from his base path to avoid the tag, and, thus, is out of the base path.
Video as follows:
Alternate Link: Ump ends M's game with out of base path call against Solano near first base
