A woman needed hospital treatment for injuries caused in the robbery in Shipley on Saturday.
Police said a man and a woman were walking their dog on Bradford Road at around 11.30am when the gang attacked them and demanded money.
A West Yorkshire Police spokesperson said: "Two mobile phones were taken, as well as a wallet and a small quantity of cash.
"The woman suffered injuries which required hospital treatment.
"The suspects are believed to have ran off towards Wycliffe Gardens.
"A 15-year-old male from Bradford has been arrested in connection with this incident and has since been released under investigation."
Witnesses should call police on 101, quoting crime reference number 13180255174, or Crimestoppers, anonymously, on 0800 555111.