The kinematics of (p, pX) knockout reactions is overviewed. Consistent descriptions of the kinematical quantities for normal and inverse kinematics are given. Starting from the kinematics of p-X elastic scatterings, which are elementary processes of the (p, pX) knockout reactions, effects of the separation energy of the knocked-out particle SX, its in-nucleus momentum $\vec{k}_{F}$, and a momentum transfer q are investigated. The three quantities are called “knockout feature quantities” in this article. The main conclusions are: SX dependences of the (p, pX) kinematics are mainly through changes in the p-X center-of-momentum energy $\sqrt{s_{pX}}$ for which no difference exists between normal and inverse kinematics. Effects of longitudinal-to-the-beam component of $\vec{k}_{F}$ cause a significant difference between normal and inverse kinematics through changes in βpX and $\sqrt{s_{pX}}$. On the other hand, the transverse-to-the-beam component of $\vec{k}_{F}$ changes energy sharing between the scattered proton and the knocked-out particle in both normal and inverse kinematics.