Bradley Beal slammed the Washington Wizards' defense, saying they were unable to "guard a parked car".

Beal had a game-high 41 points but the Wizards fell to 2-7 after a 116-107 loss to the Boston Celtics in the NBA on Friday.

The Wizards have given up an average of 122.1 points per game – the worst record in the NBA – to begin the season and Beal rued their defensive efforts.

"We all know it's our defense, but I don't know why it's our defense," he told a news conference.

"At this point we can't guard a parked car."

After back-to-back losses, the Wizards are bottom of the Eastern Conference.

But Beal remains confident they can respond, having missed the playoffs in the past two seasons.

"The way we played in the second half, it was two different teams that were out there," he said.

"In the second half, we played with energy, coach put guys out there that haven't got burned all year and they gave us a spark that we needed so I think moving forward a lot of things will be changing in terms of our lineup.

"But I'm always optimistic, I'm confident in my game, I'm confident in the team I'm on, I'm always going to be for my guys and I'm always going to be confident that we can turn it around.

"Eventually you run out of games, you do run out of games so we can't keep saying, 'It's early', we can't keep saying, 'Oh, onto the next one', we've got to make that change and we've got to compete better than what we are."