TODD Blackadder called for a change to the laws governing replacements after Bath were forced to finish their 24-6 Aviva Premiership defeat by Northampton with only 14 players.

Sam Underhill was knocked out in the 68th minute while making a tackle and because all their replacements had been used, the west country club were unable to bring on a substitute for the remainder of the match.

However, a flaw in the rules means that had Underhill only departed for a head injury assessment and not lost consciousness, Bath could have brought a player back on.

"It's a funny old law when you can't replace someone because they've been knocked out," director of rugby Blackadder said.

"If a player is HIA he can come off and you can bring someone on, but because he was knocked out it means it's a permanent removal and you can't bring someone on.

"It's not great and I hope that they do review the laws. It's actually a safety thing, no team should be penalised for that. It defies logic and this has happened before, it's not a first."

Underhill had been magnificent in defence until his departure, making 23 tackles in front of Eddie Jones to strengthen his chances of continuing as England's openside for the autumn series.

"Sam just walked past and he's okay. It's just a shame because he was getting stuck in and certainly put himself out there," Blackadder said.

"Take nothing away from Northampton, that was an outstanding performance from them and it shows how tough the competition is going to be.

"I'm disappointed when we don't perform but when you're beaten by a better side you can accept that, and we can accept this."

Northampton placed further distance between themselves and their opening-weekend rout by Saracens at Twickenham.

First Leicester were dispatched at Franklin's Gardens and then previously unbeaten Bath were over-run, tries from Courtney Lawes, a brace by David Ribbans and one from George North securing a bonus point that left boss Jim Mallinder feeling vindicated.

"Yes Saracens two weeks ago seems a long time ago, but you remember what people say. You read things and hear what people say and it hurts. And it hurts the team," Mallinder said.

"We needed a reaction last weekend and we got that. We needed to back up and we continued in that vein.

"We've shown that when we get it right, we're a difficult team to beat. Winning at home is very important and we've done that in these two games."