A search is presented for the pair production of heavy vectorlike quarks (VLQs) that each decay into a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>W</a:mi></a:math> boson and a light quark. This study focuses on events where one <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>W</c:mi></c:math> boson decays into leptons and the other into hadrons. The search analyzed <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mn>140</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:msup><e:mi>fb</e:mi><e:mrow><e:mo>−</e:mo><e:mn>1</e:mn></e:mrow></e:msup></e:math> of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>p</g:mi><g:mi>p</g:mi></g:math> collision data with <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msqrt><i:mi>s</i:mi></i:msqrt><i:mo>=</i:mo><i:mn>13</i:mn><i:mtext> </i:mtext><i:mtext> </i:mtext><i:mi>TeV</i:mi></i:math>, recorded by the ATLAS detector from 2015 to 2018 during run 2 of the Large Hadron Collider. The final state is characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum, multiple small-radius jets, and a single large-radius jet identified as originating from the hadronic decay of a boosted <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mi>W</k:mi></k:math> boson. With higher center-of-mass energy and integrated luminosity than in the run 1 search, and improved analysis tools, this analysis excludes VLQs (<m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mi>Q</m:mi></m:math>) with masses below 1530 GeV at 95% confidence level for the branching ratio <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mi mathvariant="script">B</o:mi><o:mo stretchy="false">(</o:mo><o:mi>Q</o:mi><o:mo stretchy="false">→</o:mo><o:mi>W</o:mi><o:mi>q</o:mi><o:mo stretchy="false">)</o:mo><o:mo>=</o:mo><o:mn>1</o:mn></o:math>, an improvement of 840 GeV on the previous ATLAS limit. © 2024 CERN, for the ATLAS Collaboration 2024 CERN