He overextended himself when he accepted the additional assignment.
Examples of overextend
overextend
Watch your expenditures, stick to your budget, and don't overextend your credit.
From the kansas.com
The company says it has no interest in making students overextend themselves.
From the usatoday.com
Keep distance, don't overextend, attack Jackson's poorly defended legs when he can.
From the sportsillustrated.cnn.com
If you do overextend a pure EV's battery, a flatbed truck is in your future.
From the bloomberg.com
It zigs and zags, causing even mighty empires to fall when they overextend themselves.
From the washingtonpost.com
He is quick enough to handle most pass rushers when he doesn't overextend.
From the sportingnews.com
You will face opposition if you take on too much or overextend your budget.
From the suntimes.com
You don't want to overextend yourself and later, have egg on your face.
From the suntimes.com
You don't need to overextend yourself to the point that you never relax.
From the cnn.com
More examples
Overstrain: strain excessively; "He overextended himself when he accepted the additional assignment"
To expand or extend to an excessive degree, especially to do so beyond a safe limit
(overextension) The state or quality of being overextended
(Overextended) A position where a player has moved a piece or group of pieces (usually pawns) away from the rest in such a way that they are too difficult to defend.
(Overextended) A position that is weak due to an unsuccessful attack or combination.
(Overextension) When a player rushes to get his Pawns out into the thick of the action, without developing a solid defensive structure and, at the same time, leaving channels open to attack from the enemy, he is said to have Overextended.
(Overextension) When space is gained too fast. By rushing his Pawns forward and trying to control a lot of territory, a player can leave weaknesses in his camp or can weaken the advanced Pawns themselves. He is then said to have overextended his position.
(overextension) The use, by a young child, of a single word to cover many different things.