As documented by Rolling Stone, Lindsey Buckingham hit a chair for some beats. Producer Ken Caillat shared:

Lindsey was the accent king. He could accent with guitars, he could accent with toms, he could accent with Naugahyde chairs.

Producer Kevin Caillat told Music Radar:

We called it ‘Strummer.’ Before Lindsey had the structure and the words, he would strum his guitar very very hard go these chords. I always thought he’d turn it all into a song.[…] Originally, John McVie had an amazing, flowing and melodic bass part. Lindsey had a problem with that. It took him a while, but eventually, while John was on vacation, he put down his own bassline, one that was very simple, just quarter notes.

Rolling Stone named it the #22 greatest Fleetwood Mac song, saying:

Provisionally titled ‘Strummer,’ the opening track on Rumours began as an instrumental, apparently because Buckingham didn’t want to worry Nicks with its wounded lyrics. Intrigued by the chugging rhythms found in the Bee Gees’ then-current hit ‘Jive Talkin’,’ Buckingham sought to inject a slight disco groove into the song. To achieve the desired percussive effect, he pounded the seat of a Naugahyde chair found in the studio. ‘Lindsey was the accent king,’ Ken Caillat marveled. ‘He could accent with guitars, he could accent with toms, he could accent with Naugahyde chairs.’