4 tackles for Gawn.
The definition of a tackle is...
When a player stops an opposition player with possession of the ball from getting his kick or handball away in a legal manner, or reduces the effectiveness of the opposition's disposal.
So to get a tackle stat, you don't necessarily have to wrap the bloke up.
For example, during the second term Oliver stuck out an arm which made contact with Amon (I think) as he was getting a handle away, the hand ball ineffective as it went to a Melbourne player, this resulted as a tackle stat for Oliver.
EDIT: 6 of Gawn's 7 possessions have been contested, which helps also.