stop dead / right in one's tracks

/stˈɒp dˈɛd ɔː ɹˈaɪt ɔːɹ ɪn wˈɒnz tɹˈaks/

/stˈɑːp dˈɛd ɔːɹ ɹˈaɪt ɔːɹ ɪn wˈʌnz tɹˈæks/

to stop dead / right in one's tracks

to suddenly stop moving or doing something due to being extremely surprised, frightened, or impressed