The phrase "a rock act" is correct and usable in written English.
It can be used to refer to a musical group or performance that plays rock music, typically in the context of concerts or music festivals.
Example: "The festival lineup includes a rock act that has gained popularity over the past year."
Alternatives: "a rock band" or "a rock performance".
She did a rock act after performances of "Evita".
It was Mike Appel, Springsteen's first manager, who back in the early 1970s said that "Bruce Springsteen isn't a rock act – he's a religion".
Should Glastonbury bosses announce that the Queen of Pop will be taking over from the Foos, there will inevitably be a backlash from those wanting to see a rock act.
He persisted, located their manager, Brian Epstein, and made him a deal for Feb. 12, 1964: $6,500 for two shows (a bargain! Garland commanded $25,000!) at Carnegie Hall, which had never hosted a rock act.
If Dean's campaign were a rock act, it would have been Rage Against the Machine, descending on urban areas like Iowa City and Cedar Rapids with heat and noise, drawing surging crowds at every stop.
Now, in its beautiful lakeside location in Henham Park, Suffolk, it has become perfectly normal to catch a renowned classical act – piano virtuoso Lang Lang's performance drew a huge crowd in 2012 – and then cross over the bridge to see a rock act.
Guitarist Ritchie Blackmore was a stalwart in a hard rock act that competed with Led Zeppelin and Black Sabbath for the loyalty of metal fans.
New Jersey spawned five Top 10 singles, a record for a hard rock act.
Mötley Crüe with Girls, Girls, Girls (1987) continued their commercial success and Def Leppard with Hysteria (1987) hit their commercial peak, the latter producing seven hit singles (a record for a hard rock act).
The sole booker of A-list rock acts is a seasonal one, Jones Beach Theater.
To Latin Americans, the band is a popular rock act with some cleverness -- an Offspring or a Beck.
