A golf club head includes a club body having a crown opposite a sole, a toe end opposite a heel end, a back end, and a hosel. A first magnet is coupled to the club body. A second magnet selectively engages the first magnet, such that in a first configuration the first and second magnets attract, and in a second configuration the first and second magnets do not attract, wherein the second magnet is configured to rotate relative to the first magnet between the first configuration and the second configuration.

Devices systems and methods are disclosed. Among other things, the devices systems and methods can facilitate ergonomic gripping of a handle; conform to the shape of a wrist; enhance golf techniques or performance; enhance racket sport technique or performance; protect a head of a user engaged in contact sports or other hazardous activities; identify concussions, in some cases in substantially real time; provide sterilization of garments; control surgical robots; allow for medical treatment of multiple subjects without disrobing; provide biometric or other data; and/or be used to train muscles or body parts for, for example, performing specified tasks using a body part.

A golf club head includes a body, a recessed channel, and a weight assembly. The weight assembly has a weight, a cover, and a fastener coupling the cover to the body. The cover includes a first end, a second end, and a rabbet extending at least partially between the first end and the second end. The rabbet formed by at least two walls and sized and shaped to at least partially receive the weight and allow the weight to slide therein. One or more of the at least two walls have a retention rib extending therefrom. The retention rib is elongated in a direction between the first end and the second end and discontinuous in the elongated direction. The fastener is configured to move the cover between at least two positions, a first position whereby the weight is selectively slidable and a second position whereby the weight is secured.

Embodiments of golf club heads with energy storage characteristics are presented herein. In some embodiments, a golf club head comprises a hollow body comprising a strikeface, a heel region, a toe region opposite the heel region, a sole, a top rail and an inflection point. The inflection point provides increase bending of the strikeface thereby providing performance enhancement over clubs without an inflection point.

Provided are the golf club shaft and the golf club for offering excellent feel of swing motions without demanding fine setting while keeping advantages of the short-sized golf club shaft. The golf club shaft includes a shaft body which extends in a longitudinal direction, and a gravity center shifting member attached to the shaft body for shifting a shaft gravity center toward a distal-end side in the longitudinal direction. In the case where the shaft body is cut to have a shaft full length of 43 inches or shorter, and positions of a distal-end portion and a proximal-end portion in the longitudinal direction are defined by percentage as 0% and 100%, respectively, a position of the shaft gravity center is set to be in a range from 39% to 45%.

A golf club head includes a body, a recessed channel, and a weight assembly. The weight assembly has a weight, a cover, and a fastener coupling the cover to the body. The cover includes a first end, a second end, and a rabbet extending at least partially between the first end and the second end. The rabbet formed by at least two walls and sized and shaped to at least partially receive the weight and allow the weight to slide therein. One or more of the at least two walls have a retention rib extending therefrom. The retention rib is elongated in a direction between the first end and the second end and discontinuous in the elongated direction. The fastener is configured to move the cover between at least two positions, a first position whereby the weight is selectively slidable and a second position whereby the weight is secured.

A swing practice device for emitting light at impact through self-generation enables an impact moment to be checked with the naked eyes without needing a battery by emitting light at an impact time point through self-generation during swinging by using a golf club, a baseball bat, and the like. The swing practice device includes a power generation magnet provided to a shaft so as to slide in the longitudinal direction of the shaft during swinging; a power generation coil provided on the circumference of a section in which the power generation magnet moves; a light-emitting lamp connected to the power generation coil so as to be turned on by the movement of the power generation magnet; and a magnet control means for preventing the movement of the power generation magnet at a set swing speed or lower.

A golf club head is provided with a body that has an address position with a zero degree bounce portion on the sole and a center sole position with a multi-relief surface of the sole having a negative bounce portion. The negative bounce portion may comprise a negative 0.5 to a negative 4.0 degree surface. In one embodiment, the multi-relief surface may comprise the negative bounce portion and a cutaway portion extending to the back of the sole, which may have a depth of about 0.05 to 0.5 inch from a regular sole surface. In another embodiment, the golf club head includes a weight system to adjust the center of gravity. In one embodiment, the weight system is a tube having a weight at one end that may be inserted into the golf club head to move the center of gravity at least forward and backward within 6 mm and up and down within 6 mm. Preferably, the tube is angled downward toward the face by at least 3 degrees.

Some embodiments include a club head for adjusting vertical spin of a golf ball. Other embodiments of related systems and methods are also disclosed.

An apparatus for engagement with a barrel of a bat includes a cup and at least one cover. The cup is secured for securement to a distal end of the barrel of the bat. The cup defines a cavity and includes a first connector portion. The at least one cover has a second connector portion cooperating with the first connector portion to releasably secure the cover to the cup over the cavity.