The Milwaukee Bucks staged an unprecedented boycott over the police shooting of an unarmed black man on Wednesday, forcing the NBA to halt its playoff schedule and prompting a wave of walkouts by teams across other leagues.

The NBA said it had postponed its entire slate of Wednesday fixtures after the Bucks refused to play game five of their Eastern Conference first-round series against the Orlando Magic in protest at the shooting of African-American Jacob Blake in Wisconsin on Sunday.

Blake was seriously injured after being shot in the back seven times by police officers in a confrontation captured in video footage.

"Over the last few days in our home state of Wisconsin, we've seen the horrendous video of Jacob Blake being shot in the back seven times by a police officer in Kenosha, and the additional shooting of protestors," the Bucks players said in a statement explaining their boycott.

"Despite the overwhelming plea for change, there has been no action, so our focus today cannot be on basketball."

The Bucks' no-show prompted the NBA to scrap two other games scheduled for Wednesday, Houston's clash with Oklahoma City Thunder and the Los Angeles Lakers' matchup with the Portland Trail Blazers.

The boycotts spread to other sports, with Major League Baseball's Milwaukee Brewers opting not to play their game against the Cincinnati Reds. Other baseball games were also postponed.

The Women's NBA also postponed its scheduled fixtures for Wednesday while at least two Major League Soccer fixtures were also reportedly scrapped.

Dramatic escalation

The NBA postponements marked a dramatic escalation in the league's calls for racial justice, which have reverberated across the sport in the months since the killing of unarmed black man George Floyd by police in Minneapolis in May.

Los Angeles Lakers superstar LeBron James voiced solidarity with the decision in a tweet shortly after the Bucks boycott.

"WE DEMAND CHANGE. SICK OF IT," James wrote.

The NBA's players union also backed the protest.

"The players have, once again, made it clear -- they will not be silent on this issue," National Basketball Players Association executive director Michele Roberts said in a statement.

A renewed wave of anger had swept the NBA after Sunday's shooting of Blake.

Referees huddled at the edge of an empty court Wednesday as the Milwaukee Bucks and Orlando Magic did not arrive for the scheduled start of their NBA playoff contest
Referees huddled at the edge of an empty court Wednesday as the Milwaukee Bucks and Orlando Magic did not arrive for the scheduled start of their NBA playoff contest GETTY IMAGES NORTH AMERICA / Kevin C. Cox

The 29-year-old was shot repeatedly in the back as he attempted to get into a car containing his three children.

Protests have erupted in Kenosha since the shooting, with two people killed after a man opened fire on demonstrators with an assault rifle on Tuesday.

'Horrifying, maddening'

The NBA's coronavirus-halted season resumed last month in Orlando against the backdrop of nationwide protests following Floyd's death.

NBA teams have knelt in protest during the pre-match playing of the US national anthem while the words "Black Lives Matter" have been painted onto each court staging games in Florida.

Players, many of whom took part in protests against Floyd's killing, have been allowed to wear jerseys bearing social justice messages.

The first hints of boycotts over Blake's shooting came from Toronto Raptors coach Nick Nurse, who revealed that his players had discussed refusing to play their game with Boston on Thursday.

Boston Celtics coach Brad Stevens, meanwhile, said Blake's shooting, captured on video, was "horrifying".

"We talked about it in our team meeting," Stevens said on Wednesday.

"Our thoughts are with Jacob Blake and his family and obviously that video was horrifying, awful. To think of three kids being in that car, it's ridiculous.

"These are hard times. With the pandemic going on, with this constant wave of inequality -- it's maddening."

Los Angeles Clippers coach Doc Rivers contrasted the latest shooting with the fearful rhetoric at this week's Republican Party convention.

"All you hear is Donald Trump and all of them talking about fear," Rivers said in remarks on Tuesday.

"We're the ones getting killed. We're the ones getting shot. We're the ones that are denied to live in certain communities.

"We've been hung, we've been shot. All you do is keep hearing about fear. It's amazing to me why we keep loving this country and this country does not love us back."