Strong's 2139 (εὐπερίστατος)

which doth so easily beset

well standing around, i.e. (a competitor) thwarting (a racer) in every direction (figuratively, of sin in genitive case)

from G2095 (εὖ) and a derivative of a presumed compound of G4012 (περί) and G2476 (ἵστημι);