|Wainwright's glove is possessed...by the ball.|
(A) As occurred, is Foster's (and the Replay Official)'s call correct?
(B) B1 Loney runs to second base as the glove comes off.
(C) All else equal, the third baseman standing next to the play throws his own glove off and puts his hand inside Wainwright's glove, so as to securely hold it, as Cespedes remains standing with his foot in contact with the ball-possessing glove (e.g., Cespedes is not touching the base).
(D) All else equal to [C], except the third baseman retains his glove and simply grabs Wainwright's glove from under Cespedes using his free hand. When he pulls the glove up, it is apparent that the baseball is securely lodged within the closed glove.
Answer: (A) Foster's ruling is correct. The runner is safe. The fielder is not considered as "holding the ball securely and firmly in his hand or glove" if he is not wearing his glove, in a similar vein as dropping the ball immediately following his touching a runner.
(B) The play is live—there is no interference on the runner's part—and B1's advance will stand.
(C) & (D) The definition of "tag" simply requires that the ball be held securely and firmly in hand or glove. If the fielder demonstrates secure and firm possession of the ball (or of the glove, which in turn, securely holds the ball) and tags the runner off his base, the runner is out.
Official Baseball Rules Library
OBR 5.09(b)(4): "Any runner is out when—He is tagged, when the ball is alive, while off his base."
Definition of Terms (Tag): "A TAG is the action of a fielder in touching a base with his body while holding the ball securely and firmly in his hand or glove; or touching a runner with the ball, or with his hand or glove holding the ball (not including hanging laces alone), while holding the ball securely and firmly in his hand or glove. It is not a tag, however, if simultaneously or immediately following his touching a base or touching a runner, the fielder drops the ball. In establishing the validity of the tag, the fielder shall hold the ball long enough to prove that he has complete control of the ball. If the fielder has made a tag and drops the ball while in the act of making a throw following the tag, the tag shall be adjudged to have been made."
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Alternate Link: Baserunner steps on fielder's glove, knocking it off his hand (NYM)