The Sega Genesis Team Player is a multiplayer adaptor allowing additional controllers to be plugged into the Sega Genesis base unit.
There are two versions of this device, distinguished by a single cable (original version) or two cables (second version).
The first version of Team Player (model code MK-1654), named Mega Drive 4-Player Adaptor in Europe and Sega Tap (セガタップ) in Japan, has four ports on the front for controllers, and a single cable at the rear to plug into one of the Genesis console controller ports. The second port on the Genesis base unit is thus free for a fifth controller, or a second Team Player device, potentially allowing up to 8 controllers to connect simultaneously.
A slider on the top of the first version of Team Player can be toggled between 'Multi' mode where all four ports are active, or numbers 1-4 to select use of only a single controller port. Console users could thus for example connect different types of controller (standard controller, mouse, etc) to the Team Player and use the switch to easily change between devices without needing to unplug any cables.
This first version of Team Player was not universally compatible with all Sega Genesis games as Electronic Arts had released their own 4 Way Play peripheral, and certain EA games did not offer support to Team Player.
A second version of Team Player (model MK-1647), named Mega Drive Multiplayer in Europe and Sega Tap (セガタップ) in Japan, was released and this version does work with the previously-problematic EA games.
This upgraded Team Player has a second cable and an additional option on the slider switch of 'Extra'. As well as all the same single-cable functions of the original Team Player, by plugging both cables into the Genesis unit and selecting 'Extra' this allows compatibility with the EA games that the original Team Player does not support.