Commercially, "Sledgehammer" peaked at number 40 on the Billboard Hot 100, making it Fifth Harmony's first top 40 entry in the United States.

[1] According to music sheet published at Musicnotes.com by BMG Rights Management, "Sledgehammer" is written in the key of G major and is set in a 44 common time at 100 bpm with an upbeat pop melody.

Jason Lipshutz of Billboard praised the song's "EDM-meets-new-wave beat" and its "immediate hook", believing that "Sledgehammer" is "the best pop track about the physical effects of lovesickness since Demi Lovato's "Heart Attack" (2013)".

[3] Jessica Hyndman from MTV noted that "'Sledgehammer' takes on a fun pop vibe" that lacked in the group's previous single, "Boss".

She praised the group's performance, commending that their distinctive voices sound "perfectly", but expressed that the single fell "completely into average territory.

Neid further commented on how their visuals were not as "sexy" as the music video for their 2016 single "Work from Home", but served as a "joyful and chic" reminder of their "youthful beginnings.

[11] Lipshutz stated that though one of the lines is "more than a bit confusing", the group manage to "sell their tale of unsaid infatuation with dedicated melismas and gooey production".

[11] In 2017, Billboard ranked "Sledgehammer" at number 57 on its list of 100 Greatest Girl Group Songs of All Time: Critics' Picks.

This marked Fifth Harmony's best week sales, as well as their highest-charting single and first top 40 hit;[16] It has since been surpassed by "Worth It" (2015) and "Work from Home" (2016).

[21] The video begins with the members of Fifth Harmony standing in a background of white and blue shades, where Camila Cabello takes her pulse, the band starts dancing and the screen goes dark.

The group is subsequently standing in a pyramid stair, with Cabello moving her hands in rhythm of the song before switching back to the prior scene.

Following this, the screen goes dark several times, switching from a shot of a shirtless man moving a sledgehammer and the members in the white and blue shade background.

[22] The next scene turns into color, revealing the faces of the group for the first time, with each pounding their heart with their hands as the lyric "If you could take my pulse right now, it would feel like a sledgehammer" is sung.