England's Jacks says players back under-fire skipper Brook '100 percent'
The 26-year-old Brook, in charge at a global tournament for the first time, has recently been in the spotlight for all the wrong reasons.
He last month had to apologise for being involved in an altercation with a nightclub bouncer during England's white ball tour of New Zealand last year, something that had been a "terrible mistake".
Jacks has been close to Brook since they were room-mates with England Under-19s.
"Obviously, it's been a tough time and that's been well documented in the media," Jacks told reporters ahead of team training in Mumbai on the eve of the tournament.
"I wasn't actually in New Zealand, so I didn't know anything about it.
"He's obviously made the wrong decision, but he's accepted that. He's obviously making amends on the pitch, and we all back him 100 percent."
Brook, a richly gifted run-scorer, has an early chance to shift the focus back on to his batting in England's opening match against Nepal in Mumbai on Sunday.
"He wants his cricket to do the talking," said Jacks.
England come into the World Cup in form and heartened by a 3-0 T20 series win in Sri Lanka this week.
In the preceding ODI series against the same opposition, the explosive Brook bludgeoned 136 off just 66 balls.
"It's not so much we are taking momentum from that, but team unity, feeling strong within ourselves," said Jacks.
"We have been performing well over the last 12 months, since Harry's become captain, and we're very happy with that.
"What we did in the last few weeks in Sri Lanka is another stepping stone.
"We come into here full of confidence and belief that we can go a long way in this tournament.
"But that doesn't guarantee us anything. We know that there's amazing teams in this World Cup."
"India, on home soil, I think everyone knows who's favorites."
England are expected to make the Super Eight stage from a Group C that also features two-time winners West Indies, debutants Italy and Scotland.