An adhesive for a tennis ball of the present disclosure includes base rubber and a filler. The base rubber contains, as a main component thereof, liquid rubber having a number average molecular weight of not less than 10,000. The filler has an average nitrogen specific surface area of not less than 40 m.sup.2/g. A tennis ball of the present disclosure includes a hollow core made of a rubber material. The core includes two hemispherical half cores. The two half cores are adhered to each other by using the adhesive for a tennis ball.

An adhesive for a tennis ball includes base rubber. The base rubber contains, as a main component thereof, liquid rubber having a number average molecular weight of not less than 10,000. The adhesive has a shear viscosity of not greater than 2,000 Pa.Math.s. A tennis ball includes a hollow core made of a rubber material. The core includes two hemispherical half cores. The two half cores are adhered to each other by using the adhesive for a tennis ball.

An aqueous adhesive for rubber of the present disclosure includes: a base agent containing rubber latex as a main component thereof; and an organic solvent that causes swelling of a rubber component in the rubber latex. An amount of the organic solvent in the aqueous adhesive for rubber is not less than 25% by mass and not greater than 60% by mass of a total amount of the base agent and the organic solvent. A boiling point of the organic solvent is preferably not higher than 140° C. A tennis ball of the present disclosure includes a hollow core made of a rubber material. The hollow core includes two hemispherical half cores. The two half cores are adhered to each other by using the aqueous adhesive for rubber.

A let detection system includes a sensor including an accelerometer attached to a tennis net. The sensor is in wireless communication with an umpire device able to send a message to the sensor, wherein the message causes the sensor to calibrate and begin monitoring for a let. The sensor determines a three-dimensional (3D) vector representing the gravity acting on the sensor as a baseline. When the sensor detects vertical acceleration of the net relative to the baseline and the vertical motion is above a preset threshold, the sensor automatically transmits a let notification message to the umpire device.

A method includes obtaining position information relating to an object in a sporting event, determining, based on the position information, that a start event has occurred, wherein the start event indicates a start of play of the sporting event, and generating, according to a result of the determination, an instruction to start storing position information relating to the object.

In a first aspect, a method for monitoring a golf swing is provided that includes coupling a mobile telephone to a golf club and employing the mobile telephone coupled to the golf club to monitor acceleration of the mobile telephone as the mobile telephone swings while a user swings the golf club, collect acceleration information based on the monitored acceleration of the mobile telephone as the mobile telephone swings, analyze the collected acceleration information to determine one or more characteristics of the golf swing based on the collected acceleration information, and output information regarding the one or more characteristics of the golf swing on the display of the mobile telephone. Numerous other aspects are provided.

A bag includes a main compartment configured to accommodate equipment, and a foldable chair compartment disposed adjacent to the main compartment. The foldable chair compartment is configured to accommodate a foldable chair in a folded configuration.

A sport apparatus, including a handle, an action portion, a connection portion connecting the handle to the action portion, at least part of the connection portion including a structural battery, the structural battery including one or more energy storage devices, each of the one or more energy storage devices having at least one anode core of a continuous carbon fiber, an electrolyte arranged on the at least one continuous carbon fiber core, and a cathode layer coating arranged to the at least one continuous carbon fiber core on the electrolyte, and at least one sensor unit electrically connected to the energy storage devices, the at least one sensor unit providing signals related to use of the sport apparatus.

A method for portable drill instruction for a sport can include: capturing a live video of a player of the sport in a venue for the sport playing a ball launched from a ball machine during a training drill for the player conducted in the venue; determining in response to the live video whether or not the player satisfies a training goal of the training drill when playing the ball; and providing a real-time feedback to the player during the training drill that indicates to the player whether or not the training goal is satisfied.

A wearable training apparatus has a vision-control assembly and a head-mounting assembly coupled to the vision-control assembly. The vision-control assembly has a see-through area corresponding to a central portion of the human field of vision (FOV), and a vision-blocking area for blocking the human peripheral FOV except the central portion thereof. The wearable training apparatus may be in the form of a pair of eyeglasses with lenses provided with reduced FOV or alternatively, may be in the form of a goggle with reduced FOV. A training system may comprise one or more wearable training apparatus, one or more imaging devices for recording images and/or video streams of the performance of users wearing the training apparatuses, and one or more computing devices for playing back and analyzing the recorded images and/or video streams.