jats:titleAbstract</jats:title>jats:pThe energy response of the ATLAS calorimeter is measured for single charged pions with transverse momentum in the range jats:inline-formulajats:alternativesjats:tex-math$$10<p_\text {T}<300$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:mn10</mml:mn> mml:mo<</mml:mo> mml:msub mml:mip</mml:mi> mml:mtextT</mml:mtext> </mml:msub> mml:mo<</mml:mo> mml:mn300</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> GeV. The measurement is performed using 139 jats:inline-formulajats:alternativesjats:tex-math$$\text {fb}^{-1}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:msup mml:mtextfb</mml:mtext> mml:mrow mml:mo-</mml:mo> mml:mn1</mml:mn> </mml:mrow> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula> of LHC proton–proton collision data at jats:inline-formulajats:alternativesjats:tex-math$$\sqrt{s}=13$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:msqrt mml:mis</mml:mi> </mml:msqrt> mml:mo=</mml:mo> mml:mn13</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> TeV taken in Run 2 by the ATLAS detector. Charged pions originating from jats:inline-formulajats:alternativesjats:tex-math$$\tau $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:miτ</mml:mi> </mml:math></jats:alternatives></jats:inline-formula>-lepton decays are used to provide a sample of high-jats:inline-formulajats:alternativesjats:tex-math$$p_{\text {T}}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:msub mml:mip</mml:mi> mml:mtextT</mml:mtext> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula> isolated particles, where the composition is known, to test an energy regime that has not previously been probed by in situ single-particle measurements. The calorimeter response to single-pions is observed to be overestimated by jats:inline-formulajats:alternativesjats:tex-math$${\sim }2%$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:mo∼</mml:mo> mml:mn2</mml:mn> mml:mo%</mml:mo> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> across a large part of the jats:inline-formulajats:alternativesjats:tex-math$$p_{\text {T}}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:msub mml:mip</mml:mi> mml:mtextT</mml:mtext> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula> spectrum in the central region and underestimated by jats:inline-formulajats:alternativesjats:tex-math$${\sim }4%$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:mo∼</mml:mo> mml:mn4</mml:mn> mml:mo%</mml:mo> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> in the endcaps in the ATLAS simulation. The uncertainties in the measurements are jats:inline-formulajats:alternativesjats:tex-math$${\lesssim }1%$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:mo≲</mml:mo> mml:mn1</mml:mn> mml:mo%</mml:mo> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> for jats:inline-formulajats:alternativesjats:tex-math$$15<p_\text {T}<185$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:mn15</mml:mn> mml:mo<</mml:mo> mml:msub mml:mip</mml:mi> mml:mtextT</mml:mtext> </mml:msub> mml:mo<</mml:mo> mml:mn185</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> GeV in the central region. To investigate the source of the discrepancies, the width of the distribution of the ratio of calorimeter energy to track momentum, the energies per layer and response in the hadronic calorimeter are also compared between data and simulation.</jats:p>