Buuxi weedha soo socota: Arnold oo u dhashay Needham, Massachusetts, ayaa ka qaybgalay oo ka ciyaaray hockey dugsiga sare ee Noble iyo Greenough School iyo barnaamijka Boston Junior Bruins ka hor inta uusan ku biirin Barnaamijka Horumarinta Kooxda Qaranka ee USA Hockey xilli ciyaareedkii 2009-10. Heerkii U-17, Arnold wuxuu ahaa kabtanka kooxda xulashada ee ka qayb gashay tartan shan dal oo ka dhacay Slovakia; waxaa loo magacaabay ciyaaryahanka ugu qiimaha badan tartanka. Sanadkii 2010-kii, Arnold wuxuu saddex dhibcood ka helay lix ciyaarood oo uu la yeeshay Kooxda Qaranka ee Horumarinta Barnaamijka, oo matalayay Mareykanka, wuxuu ku guuleystay billad dahab ah. Marka la eego
2010 National Hockey League (NHL) Entry Draft, Arnold waxaa loo doortay wareega afaraad, 108aad guud ahaan, Calgary Flames.