sideline  
 noun [ C ] uk/ˈsaɪd.laɪn/ us/ˈsaɪd.laɪn/
  (JOB)      
  副业,兼职工作
an activity that you do as well as your main job
  Jim works in a bank, but teaches French in the evenings as a sideline. 吉姆在银行工作,但他在晚上兼职教法语。 
   (SPORT)      
 mainly US (UK usually touchline)(运动场地上的)边线 
a line that shows the position of the side of an area where a sport is played
  The ball fell just inside/on/outside the sideline. 球正好落在了边线内/上/外。 
 Idiom   
on/from the sidelinesidiom  旁观;不参与
If you are on the sidelines or do something from the sidelines, you are not actively involved in something.
  Women have been on the political sidelines for too long - we must now work towards getting into power. 女性在政治上旁观已久——我们必须努力争取权力。 
 She could only watch from the sidelines as her brother's health deteriorated. 她只能眼睁睁地看着弟弟的身体垮下去。 
 sideline          
verb [ T ] uk/ˈsaɪd.laɪn/ us/ˈsaɪd.laɪn/
 使退出比赛,使停止参赛
If a sports player is sidelined they are prevented from playing or competing, and can only watch.
  Johnson has been sidelined through injury. 约翰逊因伤退出了比赛。 
  使靠边;使不再发挥重要作用;排挤
to stop someone taking an active and important part in something
  He was sidelined after criticizing the policy. 他对政策进行了批评以后便遭到了排挤。