How to redirect /user to /user/login
You can use rules module to create a redirect when anonymous user view the /user page.


  The Rules module allows site administrators to define conditionally
  executed actions based on occurring events (known as reactive or ECA
  rules). It's a replacement with more features for the trigger module
  in core and the successor of the Drupal 5 workflow-ng module.


You can follow below step:


Go to Administration -> Configuration -> Workflow -> Rules
Click on Add new rule link in top of page
Fill the name and select Drupal is initializing from React on Event drop down in the form and save the form.
click on Add Condition link in the page and select User has role(s) from the "Condition to add" drop-down and select anonymous user as user role and save the form.
Click on Add condition link and select "Data comparison" from the "Condition to add" drop-down and set site:current-page:path as "Data selector" and click on continue button and set 'user' in the value field and save the form.
Click on Add Action link and select Page redirect event and set user/login in the value field and save the form.