After Hawthorn won the 2008 premiership, the Hawthorn recruitment officer concentrated on the younger players in the 2009 AFL Draft. Grimley was a third-round selection (Hawthorn), No. 39 overall.
The lightly built former junior basketballer came to Hawthorn as a long-term project. After three years of development, the club started seeing good results. Grimley spent a lot of time close to goal in 2012, hoping to set himself up as a forward/ruck option. He played six games in Box Hill’s senior team early in the year but suffered a hand injury. Grimley started 2013 showing strong performances for Box Hill and the selectors were watching. Grimley was named as an emergency for the Hawks on a number of occasions in 2013. An ankle injury to David Hale helped open up an opportunity for Grimley to debut against Gold Coast in Round 9 of the 2013 AFL season. His debut started well by taking an early mark and kicking a goal with his first kick in the AFL. He finished the day with fourteen possessions and 11 hit-outs before being subbed off at three quarter time.