Reshuffle sees Steve move up to U21s.
He will combine this role with his new position as Maldon & Tiptree boss, taking over both jobs from David Wright.
Wright was appointed as Kevin Keen's assistant last week and Ball has taken his place ahead of the second half of the season.
The former U's midfielder has been in the U's Academy for three years and was working with Wayne Brown and the U18s before this switch.
He was pleased that the situation was sorted out quickly, after what has been a hectic time at the U's following Tony Humes' departure.
"It has been a manic few weeks for the club and it was important to have everything back in place as soon as possible.
"I had a good chat with Robbie and I'm really pleased and excited to be given the opportunity to take on the roles.
"We have a fantastic crop of players, at all age groups, all wanting to progress and eventually get into the first team and it's great to be able to work with the ones that are closest to achieving that."
On the Maldon & Tiptree role, Ball added: "It's an environment I have been in before and I'm looking forward to getting stuck into it again.
"There are some talented youngsters playing competitive men's football - that can only be good for their development."