[en] Standard neoclassical transport theories only consider transport associated with the standard thermodynamic forces, density gradient, temperature gradient and toroidal electric field. In neutral beam injected (NBI) heated plasma, in addition to direct collisional heating of the bulk plasma, there can be an additional thermodynamic force associated with momentum transfer from beam ions to the background plasma. Parallel momentum exchange between beam and thermal ions can drive poloidal rotation in addition to the standard temperature-gradient-driven one. This additional poloidal rotation can transfer energy between thermal energy and rotational energy. Usually energy is transferred to thermal energy via viscous heating. In addition to viscous heating, there is also a heat pinch effect due to momentum transfer from beam to thermal ions. This driven thermal ion energy flux is inward in the case of co-injection, and can be significantly larger than the standard neoclassical heat flux. The physics of this heat pinch is similar to the Ware pinch, but the former is more important in strongly NBI heated plasma. The resultant thermal ion energy balance equation (including standard neoclassical heat conduction, beam-driven viscous heating, direct heating and beam-driven heat pinch) can be solved in steady state to determine the equilibrium temperature profile. The only steady state solution to this equation is T_i ∼ r^-3, which implies thermal runaway close to the magnetic axis. The main cause of this runaway of central temperature is that the beam-driven inward heat pinch is dominant over standard conduction close to the magnetic axis. The authors conjecture that this thermal runaway in the case of co-injection may be the principal reason for the rapid increase of central temperature, the peaked ion temperature profile in the core region and the very low inferred ion thermal diffusivity in the Hot Ion H-modes in DIII-D