Given the question: Found the following article online, use it to answer the question: What is the last name of the person whose guitar technician played rhythm guitar on several songs?  Metallica opted for extensive touring instead of releasing a single or video to promote the album. Metallica spent March to August 1986 touring as the opening act for Ozzy Osbourne in the United States, the first tour Metallica played to arena-sized audiences. During sound checks, the group played riffs from Osbourne's previous band Black Sabbath, which Osbourne perceived as a mockery toward him. Referring to that occasion, Ulrich stated that Metallica was honored to play with Osbourne, who treated the band well on the tour. Metallica was noted by the media for its excessive drinking habit while touring and earned the nickname "Alcoholica". The band members occasionally wore satirical T-shirts reading "Alcoholica/Drank 'Em All". The band usually played a 45-minute set often followed by an encore. According to Ulrich, the audiences in bigger cities were already familiar with Metallica's music, unlike in the smaller towns they've visited. "In the B-markets, people really don't know what we're all about. But after 45 or 50 minutes we can tell we've won them over. And fans who come to hear Ozzy go home liking Metallica." Metallica won over Osbourne's fans and slowly began to establish a mainstream following.The tour, however, was notable for several incidents. Hetfield broke his wrist in a mid-tour skateboarding accident, and his guitar technician John Marshall played rhythm guitar on several dates. The European leg of the Damage, Inc. Tour commenced in September, with Anthrax as the supporting band. After the performance of September 26 in Stockholm, the band's bus rolled over on a stretch of icy road the following morning. Burton was thrown through a window and killed instantly. The driver was charged with manslaughter but was not convicted. The band returned to San Francisco and hired Flotsam and Jetsam bassist Jason Newsted to replace Burton. Many of the songs that appeared on the band's next album, ...And Justice for All, were composed during Burton's career with the band.
The answer is:
Hetfield