The tribunal took almost two hours to reach a verdict - twice as long as the hearing for Shiel's unusual charge relating to an incident that felled a teammate.
The Bomber veteran pushed Geelong's Mark O'Connor, causing the Cat to collide with Shiel's teammate Luamon Lual.
After a 66-minute hearing, the tribunal returned 113 minutes later with its decision to suspend Shiel for one match.
"This case is a little out of the ordinary," AFL counsel Nick Pane KC said, conceding the charge "doesn't fit neatly" in the league's gradings.
Shiel's counsel Ben Ihle KC said the charge was an over-reach.
"It is clear, in our submission, that the intention (of laws) is the protection of opposition players," Ihle said.
"And therefore the invitation that the AFL has extended to the tribunal to look beyond O'Connor, and look at the incidental consequences by Shiel's conduct to another player, is misconceived.
"Not only does it not fit neatly, to use Mr Pane's words ... this is a situation that rules do not cover."
Shiel told the hearing his intent was to mark or at worst protect the drop zone of an incoming ball.
"After I contested and got the ground ball, I was quite shocked to see another teammate on the ground," Shiel said.
"I didn't know how he got there."
Lual flipped spectacularly and landed awkwardly on his neck and shoulder, but after being assessed by medicos, returned before being substituted.
Tribunal chair Renee Enbom said the force of Shiel's push on O'Connor was "unreasonable".
"It was not conduct that a reasonable player would consider prudent," she said.
"Shiel breached his duty of care."
Essendon coach Brad Scott, previously the head of AFL football operations, earlier Tuesday said the Bombers had copped a "triple whammy" of punishment: a free kick against, Lual's injury and a tribunal case.
"We have been penalised three times without the opposition actually being the victim, as far as I can see," he told reporters before the hearing.
But GWS coach Adam Kingsley said Shiel's case was comparable with Richmond's Rhyan Mansell being banned three games by the tribunal for pushing St Kilda's Liam O'Connell into a marking contest.
The AFL cited Mansell's case as evidence during Shiel's hearing.
"I didn't like the action ... it could have ended really badly," Kingsley told Fox Footy.
But Western Bulldogs coach Luke Beveridge said Shiel's intent was key.
"I don't think he's planning to push someone into his teammate," Beveridge said.
Adelaide will later Tuesday challenge veteran Rory Laird's one-game rough conduct ban for a high bump, which currently rules him out of Saturday's vital home game against Collingwood.
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