Current quark
As current quark which are quarks in hadrons called that at high energies because of asymptotic freedom of strong interaction almost as free particles behave. A current quark mass is assigned to them - relatively small for the light up and down quarks .
However, they interact in the hadron via the exchange of gluons with virtually generated quark-antiquark pairs ( sea quarks ), so that as constituent quarks they have a significantly higher constituent quark mass , with protons about 300 MeV / c² each .