To find the origin of chaos near black hole horizon in string-theoretic<br />
AdS/CFT correspondence, we perform a chaos analysis of a suspended string in<br />
AdS black hole backgrounds. It has a definite CFT interpretation: chaos of<br />
Wilson loops, or in other words, sensitive time-evolution of a quark antiquark<br />
force in thermal gauge theories. Our nonlinear numerical simulation of the<br />
suspended Nambu-Goto string shows chaos, which would be absent in pure AdS<br />
background. The calculated Lyapunov exponent $\lambda$ satisfies the universal<br />
bound $\lambda \leq 2\pi T_{\rm H}$ for the Hawking temperature $T_{\rm H}$. We<br />
also analyze a toy model of a rectangular string probing the horizon and show<br />
that it contains a universal saddle characterized by the surface gravity $2\pi<br />
T_{\rm H}$. Our work demonstrates that the black hole horizon is the origin of<br />
the chaos, and suggests a close interplay between chaos and quark<br />
deconfinement.