This book constitutes selected and revised papers from the First International Workshop on Combating On line Ho st ile Posts in Regional Languages dur ing Emerge ncy Si tuation, CONSTRAINT 2021, Collocated with AAAI 2021, held as virtual event, in February 2021.  The 14 full papers and 9 short papers presented were thoroughly reviewed and selected from 62 qualified submissions. The papers present  interdisciplinary approaches on multilingual social media analytics and non-conventional ways of combating online hostile posts.