San Francisco-based Halo Neuroscience sell the Halo sport (749 USD), which uses transcranial direct-current stimulation (tDCS) for motor skill learning.
Their claims appear to have decent empirical backing.
Interestingly, their marketing material run the gamut of physical activity, from weightlifters, to runners, to men in polo suits playing golf. Sport activities are heterogeneous, and it is unclear how well their laboratory studies account for this heterogeneity.
Halo Neuroscience has raised 10.7M USD as of today.