Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
sideline [ˈsaɪdlaɪn] n (SPORT) бокова́я ли́ния; (fig, supplementary job) побо́чная рабо́та
to stand on the sidelines стоя́ть*(impf) в стороне́
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.