Pari gbolohun yii: Ọmọ ìlú Needham, Massachusetts, Arnold lọ sí ilé-ẹ̀kọ́ gíga, ó sì gbá hockey ní ilé-ẹ̀kọ́ Noble and Greenough School àti ilé-ẹ̀kọ́ Boston Junior Bruins kí ó tó darapọ̀ mọ́ USA Hockey National Team Development Program fún sáà 2009<unk>10. Ni ipele U-17, Arnold jẹ olori ẹgbẹ ti ẹgbẹ ti o yan ti o kopa ninu idije orilẹ-ede marun kan ni Slovakia; a pe ni oṣere ti o niyelori julọ ti idije naa. Ni 2010 IIHF World U18 Championships, Arnold ṣe igbasilẹ awọn ojuami mẹta ni awọn ere mẹfa bi National Team Development Program, ti o ṣe aṣoju fun Orilẹ Amẹrika, gba ami ẹyẹ goolu. Níbi tí
2010 National Hockey League (NHL) Entry Draft, Arnold ni won yan ni kẹrin yika, 108th gbogbo, nipa awọn Calgary Flames.