West Ham have conceded nine goals in their last five matches, but have also scored regularly. They've been actively picking up points (three wins in five matches), but remain in the relegation zone, three points behind 17th place. Manchester United boast an even more potent attack, scoring 10 goals in their last four Premier League games, but their defense has been fragile, especially away from home (21 goals conceded in 12 matches).
Their head-to-head record also confirms the trend toward mutually beneficial goals. In four of their last five league encounters, both teams have traded goals, including a 1-1 draw in December. West Ham have won their last two home games against United, demonstrating a psychological advantage and an ability to identify weaknesses in the visitors' defense.
Considering the teams' motivations (Manchester United are fighting for the top four, while West Ham are fighting to stay in the top flight), their attacking potential and their history of head-to-head encounters, it is logical to expect a goal exchange.