In rugby union, the second rower, also known as the lock, plays an important role in both the scrum and lineout. Here are some of the key responsibilities of a second rower:

1. Scrum: The second rowers form the second row of the scrum, behind the front row. They provide support and stability to the front row and help to drive the scrum forward.

2. Lineout: The second rowers are the primary jumpers in the lineout, where they aim to catch the ball thrown in by the hooker. They must be strong and athletic in order to compete for the ball with opposing players.

3. Ball carrying: Second rowers are often called upon to carry the ball forward in open play. They need to be strong and powerful runners who can break through tackles and gain ground for their team.

4. Tackling: Second rowers are also responsible for making tackles, both in open play and at the breakdown. They must be able to bring down larger players and prevent them from gaining ground.

Overall, the role of the second rower is a physically demanding one, requiring a combination of strength, agility, and endurance. They play a critical role in both the set piece and open play, and are key contributors to their team’s success.